Optical Code Division Multiple Access Based Long Reach Passive Optical Network

Tile Auhor(s) Opical Code Division Muliple Access Based Long Reach Passive Opical Nework Yoshima, Saoshi Ciaion Issue Dae Tex Version ETD URL hps://doi.org/10.18910/26174 DOI 10.18910/26174 righs

Docoral Disseraion Opical Code Division Muliple Access Based Long Reach Passive Opical Nework Saoshi Yoshima July 2013 Division of Elecrical, Elecronic, and Informaion Engineering Graduae School of Engineering Osaka Universiy

Preface This disseraion reas a long reach passive opical nework (PON) using opical code division muliple access (OCDMA) echnologies based on research he auhor carried ou during his Ph. D. sudies in he Division of Elecrical, Elecronic, and Informaion Engineering, Graduae School of Engineering, Osaka Universiy, and his enure a he Misubishi Elecric Corporaion. Chaper 1 is an inroducion of he hesis and presens he background and purpose of he sudy. The hisorical perspecive and recen invesigaions on access neworks are summarized. Opical access nework echnologies for high-speed, highly flexible, and long-reach ransmission are hen inroduced. Finally, he moivaion behind his sudy, including he reason for focusing on opical code division muliplexing (OCDM)/OCDMA, is presened. Chaper 2 gives an overview of opical encoding/decoding echniques. Opical devices for opical encoding/decoding are also described in his chaper. Here, he pros and cons are discussed from he viewpoins of he difference in characerisics for opical encoding/decoding schemes. Finally, we inroduce he properies of a muli-por encoder/decoder ha can simulaneously process several opical codes (OCs). Chaper 3 deals wih 10-Gb/s burs-mode ransmission. Firs, a 10-Gb/s burs-mode ransmier for an opical nework uni (ONU) is inroduced. The impedance conrolled DC-coupled ransmission line beween a laser diode (LD) driver and a disribued feedback LD (DFB-LD) enables boh a fas urn-on/off ime and high-launched opical power. Nex, a 10-Gb/s burs-mode receiver for an opical line erminal (OLT) is described. To mee he demand for wide dynamic range and good receiver sensiiviy, coninuous auomaic gain conrol (AGC) and auomaic hreshold conrol (ATC) funcions are adoped for he burs-mode receiver. In addiion, he configuraion of an 1/10-Gb/s dual-rae burs-mode receiver, which can be realized by uilizing a serial ype ransimpedance amplifier (TIA) and limiing amplifier (LIA), is described. The TIA and LIA swich heir ransimpedance gain, noise equivalen bandwidh, and ransien response ime by an exernal rae selec signal. The resuls described in Chaper 3 have been published in II-1, II-6, III-1, III-4, and III-5 ha are shown in he lis of publicaions by he auhor. Chaper 4 exends he 10-Gb/s ime division muliplexing (TDM) PON sysem over OCDMA (10G-TDM-OCDM-PON) using a super-srucured fiber Bragg graing (SSFBG) encoder for he ONU, a i

muli-por decoder, and a 10-Gb/s burs-mode receiver for he OLT. Then, we experimenally demonsrae TDM OCDM uplink ransmission. Wih he assisance of forward error correcion (FEC), error-free operaion can be achieved in all daa of he 10G-TDM-OCDM-PON. In addiion, we show ha he key o unprecedened symmeric uplink bandwidh is a muli-level phase-shifed encoding/decoding whereby an auo-correlaion oupu can be preferably adoped in he burs-mode receiver. The uplink hroughpu performances of he 10G-TDM-OCDM-PON are also discussed. The resuls described in Chaper 4 have been published in I-1, II-2, II-3, II-4, III-2, and III-3 ha are shown in he lis of publicaions by he auhor. Chaper 5 proposes long reach 10G-TDM-OCDM-PON sysems. To achieve long reach ransmission over a 65-km single mode fiber (SMF), hree schemes are newly adoped in addiion o 10G-TDM-OCDM-PON. Firs, a narrow band opical band pass filer (NB-OBPF), which can ailor he OC specrum, is applied for he oupu of he muli-por encoder o ransmi OC signals wihou dispersion compensaion. Second, long reach 10G-TDM-OCDM-PON can be scaled up by aggregaing 10-Gb/s TDM-PON sysems using only a muli-por encoder/decoder pair in an OLT and a remoe node (RN). The configuraion of he ONU becomes simpler han he 10G-TDM-OCDM-PON by eliminaing he encoder/decoder a each ONU. Third, an 82.5 Gsample/s over-sampling clock and daa recovery (CDR) is used for a burs-mode 3R receiver. The 10-Gb/s burs-mode 3R receiver can recover a pulse widh disored signal afer ransmission. We experimenally demonsrae full duplex 10G-TDM-OCDM-PON ransmission on a single wavelengh over a 65-km SMF wihou dispersion compensaion. Error-free operaion wih a FEC for all uplink and downlink daa can be achieved. In addiion, we discuss he causes of power penaly. The ransmission penaly has been he mos pressing issue in he consrucion of long reach 10G-TDM-OCDM-PON sysems because i is he main cause of power penaly. The resuls described in Chaper 5 have been published in I-2, II-5, and III-6 ha are shown in he lis of publicaions by he auhor. Chaper 6 summarizes he above resuls. Saoshi Yoshima July 2013 ii

Acknowledgmens The presen research has been carried ou during my enure a he Misubishi Elecric Corporaion and my docorial course a he Deparmen of Informaion and Communicaions Technology in he Division of Elecrical, Elecronic, and Informaion Engineering, Graduae School of Engineering, Osaka Universiy, under he guidance of Prof. Ken-ichi Kiayama. Firs, I would like o express my deepes sense of appreciaion o Prof. Ken-ichi Kiayama for his professional insrucion, coninuous encouragemen, and a number of simulaing discussions. His keen insigh and wealh of creaive ideas have always provided me wih precise guiding frameworks for performing my research. I have learned many valuable lessons hrough my collaboraion wih him. I have been ruly forunae o have had he opporuniy o work wih him. I am profoundly indebed o Prof. Kyo Inoue and Associae Prof. Akihiro Marua of Elecrical, Elecronic, and Informaion Engineering Division for careful reviews and commens, which have improved his disseraion. I grealy hank Associae Prof. Akihiro Marua for his invaluable guidance hroughou he work on his hesis. I am also grealy indebed o Prof. Tesuya Takine, Prof. Seiichi Sampei, Prof. Noboru Babaguchi, and Prof. Takashi Washio of Elecrical, Elecronic, and Informaion Engineering Division for giving me sufficien basic background for his hesis. I wish o express my sincere hanks o Associae Prof. Shinichi Miyamoo, Associae Prof. Takahiro Masuda, and Assisan Prof. Yuki Yoshida of Elecrical, Elecronic, and Informaion Engineering Division for providing me wih echnical advice for his hesis. I paricularly appreciae Dr. Naoya Wada, Mr. Yoshihiro Tomiyama, and Mr. Hiroyuki Sumimoo of he Phoonic Nework Sysem Laboraory, Phoonic Nework Research Insiue, he Naional Insiue of Informaion and Communicaions Technology for heir fruiful discussions and grea suppor for experimens. Special hanks go o Dr. Nobuyuki Kaaoka, who was wih he Naional Insiue of Informaion and Communicaions Technology, for his appropriae advice abou OCDMA, fruiful discussions, and heary encouragemen. I wish o express my sincere appreciaion for all he pas and presen colleagues of he Phoonic Nework iii

Laboraory in he Division of Elecrical, Elecronic, and Informaion Engineering, Graduae School of Engineering, Osaka Universiy. I grealy hank Mr. Naoki Nakagawa and Mr. Yusuke Tanaka for heir collaboraions hrough his research. I also would like o hank Dr. Kiyoshi Onohara, Dr. Kensuke Ikeda, Dr. Shoichiro Oda, Dr. Yuji Miyoshi, Mr. Taro Hamanaka, Dr. Takahiro Kodama, and Mr. Ryosuke Masumoo for fruiful discussions and coninuing friendships. I would like o hank o Prof. Gabriella Cincoi of Universiy Roma Tre for suppor wih he experimens. I would like o hank Misubishi Elecric Corporaion, in paricular he Informaion Technology R&D Cener, for providing invaluable opporuniies o devoe myself o such exciing echnological challenges. A large number of people in his company have helped me in his research. I am paricularly graeful o Dr. Shinya Fushimi for giving me he opporuniy o work owards my docorae and his generous suppor. I appreciae Dr. Takashi Mizuochi for providing me wih valuable commens from his considerable experience in he area of opical fiber communicaion, close suppor, and coninuous encouragemen. I also appreciae Mr. Masamichi Nogami for his helpful echnical advice in heoreical and experimenal research on opical ransceivers and inegraed circuis for opical fiber communicaion, especially in he area of high-speed burs-mode ransmission. I wish o express my sincere hanks o Dr. Kuniaki Mooshima, Mr. Hiroshi Ichibangase, Mr. Hioyuki Tagami, Dr. Asushi Sugiasu, Mr. Hiroshi Aruga, Mr. Akira Takahashi, Mr. Seiji Kozaki, and Dr. Hiroaki Mukai for heir echnical advice, commens, and suppor. Special hanks go o Dr. Junichi Nakagawa for providing me wih commens and advice in he area of opical access nework. I would like o express my graiude o all he pas and presen colleagues of he Opical Communicaion Technology Deparmen in he Informaion Technology R&D Cener, Misubishi Elecric Corporaion. Special hanks go o Mr. Masaki Noda, Mr. Naoki Suzuki, Mr. Toshiharu Miyahara, Mr. Saoshi Shirai, Mr. Susumu Ihara, Mr. Nobuo Ohaa, Mr. Eiesu Igawa, Mr. Kenji Ishii, Mr. Ken-ichi Kobiki, Mr. Daisuke Mia, and Mr. Tesuro Ashida, who provided me wih invaluable suggesions and devoed a lo of ime o me in fruiful discussions. Finally, I would like o hank my parens, Yuaka and Musuko, my siser, Akiko, my paernal grandmoher, Emi, and my maernal grandparens, Yasuo and Yasuyo, for heir deep undersanding, suppor, and love during he whole period of my life. iv

Conens Preface i Acknowledgmens iii Chaper 1 Inroducion 1 1.1 Demand for High-Speed Access Neworks 2 1.2 Archiecure of Opical Access Nework 4 1.3 Roadmap of Opical Access Nework 8 1.4 Purpose of This Sudy 10 1.5 Overview of he Disseraion 10 Chaper 2 Overview of Opical Code Division Muliplexing 13 2.1 Inroducion 13 2.2 Principle of Opical Encoding/Decoding 14 2.2.1 Opical Encoding 14 2.2.2 Opical Decoding 15 2.3 Opical Devices for Opical Encoding/Decoding 16 2.4 Muli-Por Encoder/Decoder 20 2.4.1 Configuraion of Muli-Por Encoder/Decoder 20 2.4.2 Correlaion Propery 22 2.5 Conclusion 26 Chaper 3 10-Gb/s Burs-Mode Transmission Technologies 27 3.1 Inroducion 27 3.2 10-Gb/s Burs-Mode Transmier Technologies 28 3.2.1 10-Gb/s Burs-Mode Transmier Configuraion 28 3.2.2 Experimenal Resuls 29 3.2.3 Analysis of Burs-Mode Performances 31 3.3 10-Gb/s Burs-Mode Receiver Technologies 32 3.3.1 Burs-Mode Receiver Configuraion 32 3.3.2 Dual-Rae Receiver Configuraion 33 3.3.3 Dual-Rae Burs-Mode Transceiver Configuraion 34 v

3.3.4 Experimenal Resuls 35 3.4 Conclusion 38 Chaper 4 10G-TDM-OCDM-PON Sysem 39 4.1 Inroducion 39 4.2 10G-TDM-OCDM-PON Sysem Configuraion 40 4.3 Burs-Mode Uplink Transmission Experimen 41 4.4 Discussion 46 4.4.1 Correlaion Performances for 10-Gb/s Burs-Mode Recepion 46 4.4.2 Uplink Throughpu Performances 47 4.5 Conclusion 49 Chaper 5 Long Reach 10G-TDM-OCDM-PON Sysem 51 5.1 Inroducion 51 5.2 Long Reach 10G-TDM-OCDM-PON Sysem Configuraion 52 5.2.1 Muli-Por Encoder/Decoder Pair a OLT and RN 53 5.2.2 Exended Reach by NB-OBPF 53 5.2.3 10-Gb/s Burs-Mode 3R Receiver 55 5.3 Full-Dulplex Transmission Experimen wihou Dispersion Compensaion 57 5.3.1 Experimenal Seup and Transmission Performance 57 5.3.2 65-km SMF Transmission wihou Dispersion Compensaion 60 5.4 Discussion on Power Penaly 63 5.5 Conclusion 65 Chaper 6 Conclusion 67 Bibliography 69 Acronyms 81 Lis of Publicaions by he Auhor 85 vi

Chaper 1 Inroducion Developmens o fiber-opic communicaion echnologies have been delivering smarer and more comforable lifesyles o people for he pas several decades [1]. In 1981, he firs fiber-opic ransmission sysems feauring a 32-Mb/s capaciy were launched in Japan [2]. A firs, hese sysems were applied only for runk ransmission. Soon afer ha, submarine ransmission was realized by fiber-opic communicaion echnologies. Since he firs insallaion of fiber-opic communicaion sysems, remarkable progress of opical fiber ransmission echnologies has been seen. For example, nowadays fiber-opic ransmission sysems wih 100-Gb/s capaciy per one wavelengh channel can be realized [3 5], bu access neworks have been consruced by wised pairs for a long ime. The remarkable expansion of Inerne services, such as video on demand, online video games, file sharing, and music disribuion, as well as he numerous social media services, has creaed a demand for high-speed access neworks. In order o mee his demand, opical access neworks sared being inroduced from he end of he 1990s. Of paricular noe are Gigabi Eherne passive opical neworks (1G-EPON) [6], which can deliver more han 1-Gb/s high-speed ransmission and provide low-cos services for residences. Due o he spread of 1G-EPON sysems, here were more han 23.2 million fiber-o-he-home (FTTH) subscribers in Japan by he end of Sepember 2012 [7]. This growh of opical access neworks comes wih he demand for access neworks ha are higher speed, more flexible, and more inelligen. 1

2 Chaper 1. Inroducion In his chaper, hisorical perspecive on access neworks, including he archiecure of opical access neworks, are inroduced. More recen and fuure opical access neworks are also reviewed. 1.1 Demand for High-Speed Access Neworks The rise of new conen-rich services and he increasing demand for faser services have driven he progress of high-speed access neworks. Nowadays, several online services are able o be uilized, including video on demand, online video games, file sharing, and music disribuion, as well as numerous social media services. These services require ransmiing no only ex-based conen bu also mulimedia conen including music and video. In order o saisfy he large bandwidh requiremens, broadband services were insalled oward he end of he 1990s in Japan. Access neworks can be mainly classified ino four ypes: copper-based digial subscriber lines (DSLs) [8, 9], which were almos asynchronous DSL (ADSL), hybrid fiber and coaxial (HFC) neworks for CATV [10], fiber opic-based fiber-o-he-x (FTTX) [11], and high-speed mobile services including 3.9-generaion mobile communicaion called long-erm evoluion (LTE) [12] and broadband wireless access (BWA) adoping he 2.5-GHz frequency band [13]. Here, he x of FTTX indicaes home (H), building (B), curb (C), and so on, depending on he nework archiecure. FTTH and FTTB mean ha he fiber reaches he boundary for he living space such as he home and he building, respecively. FTTC means ha he fiber reaches he sree cabine, which is close o he user s premises, ypically wihin several hundred meers. In all of he FTTX sysems, a meallic cable or wireless sysems such as wireless local area nework (LAN) are used for neworks beween he opical nework uni (ONU) and user erminal such as a personal compuer (PC). Figure 1.1 shows he evoluion of he number of broadband service subscribers in Japan [7]. As shown in he figure, ADSL services were commercialized in he early 2000s as he firs widespread broadband service o mee he new demand for high-speed daa communicaion neworks. The ADSL echnologies were able o realize faser daa communicaion services on he insalled meal cable han he previous inegraed services digial nework (ISDN) sysems wih 64-kb/s. The number of DSL subscribers increased o 14.5 million in he firs quarer of 2006. However, here were several issues for realizing high-speed broadband services. One was he limiaion of ransmission disance. The signal o noise raio of ADSL services is degraded due o line noise in he meallic cables, which means ha only low-speed services are provided for subscribers locaed a long disance from he cenral office (CO) of he service provider. The second issue was he limiaion of ransmission speed.

1.1. Demand for High-Speed Access Neworks 3 High-speed ADSL was realized by a muli-level modulaion forma such as 64 quadraure ampliude modulaion (QAM) and high-frequency ransmission higher han a normal voice elephony channel. However, he highes ransmission speed of ADSL was only several Mb/s due o he ransmission frequency limiaion of up o several MHz. Therefore, he number of subscribers has been decreasing since 2006. In conras, FTTH services sared o widely spread from he middle of he 2000s because hey can provide symmeric high-speed communicaion sysems more reliably han ADSL services. FTTH sysems can provide faser han 100-Mb/s high-speed symmeric ransmission services for each subscriber, 20-km long ransmission lines, and high-qualiy services. This syle of high-speed access sysem is paving he way for a new generaion of broadband services. As a resul, he number of FTTH users exceeded ha of ADSL users a he end of June 2008. Nowadays, FTTH is he mos popular broadband infrasrucure in Japan. A he end of Sepember 2012, he number of FTTH subscribers in Japan was 23.2 million. In addiion, he number of subscribers of CATV services has gradually increased. From he beginning of 2012, he number of subscribers of broadband mobile services, including he 3.9G mobile service and BWA, has rapidly increased because mobile phones wih more advanced compuing and conneciviy ( smarphones ) can access he Inerne easily and from anywhere. These broadband mobile services will play an imporan role in broadband services in he near fuure. 25 25.00 Number of subscribers (Million) 20 20.00 15 15.00 10 10.00 5 5.00 DSL FTTH CATV 3.9G Mobile BWA 0 0.00 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 Year Fig. 1.1: Number of broadband subscribers in Japan. (Based on Minisry of Inernal Affairs and Communicaions Japanese Governmen Repor)

4 Chaper 1. Inroducion 1.2 Archiecure of Opical Access Nework Figure 1.2 shows he opologies of opical access sysems [14, 15]. In general, here are hree caegories of archiecure o realize an opical access nework. One is he poin-o-poin (P2P) sysem shown in Fig. 1.2(a), which is he basic configuraion for opical access neworks. This sysem feaures a CO comprised of several media converers conneced o each residenial user. In his P2P nework, individual fibers run from a CO o each residenial home. Anoher archiecure is he poin-o-mulipoin sysem (P2MP) wih an acive swich, which is called acive sar archiecure. In his nework, only one fiber is insalled beween a CO and an acive swich, and he CO needs only one media converer o communicae wih all residenial homes. The oal cos of he acive sar archiecure is less han ha of he P2P sysem because here is only one media converer per CO and only one feeder fiber beween a CO and an acive swich. However, he acive swich requires powering and mainenance, and i should be capable of operaion over a wide emperaure range because i is an oudoor device. The oher archiecure is he P2MP wih passive devices such as opical spliers, which is called passive sar archiecure or passive opical nework (PON). In his archiecure, a CO is conneced o each residenial home via an opical power splier. In a PON sysem, subscriber equipmen, which is called an ONU, can be accommodaed by a single piece of CO equipmen called an opical line erminal (OLT). This archiecure reduces coss because a splier requires no power supply and lile mainenance. As a resul, PON sysems currenly play he main role in opical access neworks. PON sysems feaure four opical access echnologies: ime division muliple access (TDMA) [16], wavelengh division muliple access (WDMA) [17], orhogonal frequency division muliple access (OFDMA) [18], and opical code division muliple access (OCDMA) [19]. Figure 1.3 compares hese echnologies using heir schemaic represenaions. In he TDMA, each ONU upsream ime slo is conrolled by an OLT access conroller o avoid collisions. As a resul, upsream packes from he ONUs are ime-inerleaved a he power splier. The OLT receiver has o adjus is gain, hreshold, and clock synchronizaion o receive burs signals because he ransmission loss and ime slo of each ONU are differen [20 22]. The TDM-PON plays he main role in opical access sysems due o low cos capable equipmen. Alhough he cos of a burs-mode receiver and an access conroller is higher han ha of oher equipmen, hey can be shared by all of he residenial users. There has been a remendous amoun of research and developmen on TDMA sysems, going all he way back o he firs proposal of TDM-PON sysems back in 1987 [23, 24]. Early experimens and field rials were performed using he synchronous ransfer mode (STM) and he

1.2. Archiecure of Opical Access Nework 5 asynchronous ransfer mode (ATM). In Japan, he firs commercial sysem was launched as a STM-PON wih 16-Mb/s in 1997 [25]. Afer ha, he broadband PON (B-PON) wih 622-Mb/s [26], 1G-EPON wih 1.25-Gb/s [6], and Gigabi-capable PON (G-PON) wih 2.5-Gb/s [27] capaciies were sandardized in 2001, 2004, and 2004, respecively. These sysems have also been commercially launched all over he world for use in FTTX sysems. In WDMA neworks, a wavelengh channel is assigned o each ONU. There is no ineracion or coupling beween subscribers. As a resul, each subscriber ges a dedicaed poin-o-poin pah o an OLT. In a ypical WDMA, wavelengh channels are muliplexed or demuliplexed by an arrayed waveguide graing (AWG) insead of an opical power splier, as shown in Fig. 1.3(b). WDMA neworks require wavelengh seleced ransceivers for each ONU. This colored ONU increases he nework cos. To resolve his, research on WDMA neworks wih an injecion-locked Fabry-Pero laser diode or a reflecive semiconducor opical amplifier (RSOA) as a colorless ONU ransmier have been energeically pursued [28 30]. However, a presen, here have only been field rials in limied regions such as Korea, and hus far here has been no large scale commercial deploymen. In OFDMA neworks, he overall bandwidh is divided ino orhogonal subcarriers. Each ONU is allocaed one or more subcarriers ha can be realized by fas Fourier ransform (FFT) and inverse FFT (IFFT). Differen modulaion formas can be assigned for each subcarrier based on he channel condiions and he ransmier frequency response. In addiion, he upsream bandwidh of each ONU can be changed by changing he assigned number of subcarriers. Therefore, OFDMA neworks can provide flexibiliy and scalabiliy for each ONU. OFDMA has funcioned as he major access echnology in RF communicaions such as LTE. Neverheless, is applicaion o opical communicaion is challenging because high-speed digial signal processing (DPS) is expensive for opical access neworks and he synchronizaion of muliple upsream laser frequency offse from each ONU is difficul. In recen years, several sudies have repored mehods for realizing OFDMA-PON. In 2007, 10-Gb/s opical OFDMA ransmission using a direc modulaed laser (DML) in a 2.5-GHz channel bandwidh was experimenally demonsraed offline, for he firs ime [31]. Recenly, real-ime 40-Gb/s WDM-OFDMA-PON ransmission has been demonsraed using a field programmable gae array (FPGA)-based DSP [32]. In addiion, o realize a bandwidh-elasic and power-efficien OFDMA nework, coheren inerleaved frequency division muliple access (IFDMA) has been proposed and experimenally demonsraed [33, 34]. In an OCDMA nework, upsream signal ransmission is realized by he opical encoder (ENC) and opical decoder (DEC). OCDMA can muliplex a number of channels on a single wavelengh and idenical ime slo by using differen opical codes for each channel, similar o spread-specrum wireless CDMA [35]. In conras o he frequency spread/despread, ime and/or opical frequency

6 Chaper 1. Inroducion spread/despread echniques are adoped in OCDMA. OCDMA has been sudied and experimens have been performed since he 1980s [36, 37]. Early sudies showed promise in overcoming some of he nagging drawbacks in hose days, which included laser frequency drif, broad laser line widhs, and limied hardware speeds. In recen years, coheren OCDMA has been energeically sudied in pursui of is unique characerisics such as high frequency efficiency, good correlaion performance, low signal processing laency, and asynchronous access capaciy [19]. Encoding/decoding of a coheren ime-spreading (TS)-OCDMA sysem has been realized by using compac opical passive devices such as a super-srucured fiber Bragg graing (SSFBG) [64] and/or a muli-por opical encoder/decoder in an AWG configuraion [67]. Recenly, a field rial of 3-WDM 10-OCDMA 10.71-Gb/s, asynchronous 111-km ransmission [97] and an experimenal demonsraion of asynchronous 4 40-Gb/s full-duplex ransmission [38] have been achieved. Media converer Media converer Cenral office (a) Poin-o-poin archiecure Media converer Acive swich Media converer Cenral office (b) Acive sar archiecure OLT Opical power splier ONU Cenral office (c) Passive opical nework Fig. 1.2: Archiecures of opical access nework.

1.2. Archiecure of Opical Access Nework 7 Burs-mode Tx #1 Burs-mode Rx T 1 T n Burs-mode Tx #n (a) TDMA 1 Tx #1 Rx #1 1 AWG AWG Rx #n n n 1 n Tx #n (b) WDMA Tx #1 DSP DSP Rx f Tx #n DSP subcarriers (c) OFDMA ENC #1 Tx #1 Rx #1 DEC #1 Rx #n DEC #n Code #n ENC #n Tx #n Code #1 (d) OCDMA Fig. 1.3: Opical access echnologies.

8 Chaper 1. Inroducion 1.3 Roadmap of Opical Access Nework Figure 1.4 shows he roadmap of opical access nework echnologies [45 50]. Currenly, 1-Gb/s TDM-PON sysems including 1G-EPON and G-PON have become widely spread hanks o a bi rae higher han 1.25 Gb/s, a possible number of shared users as high as 32, and a ransmission lengh of 20 km. In order o mee he demand for high-speed opical access sysems, 10-Gb/s TDM-PON sysems including 10-Gigabi Eherne PON (10G-EPON) [39, 43] and 10-Gigabi-capable PON (XG-PON) [40, 44] were sandardized in 2009 and 2010, respecively. These 10-Gb/s TDM-PON sysems are called nex-generaion PON1 (NG-PON1). For NG-PON1, he mos crucial challenge is high-speed 10-Gb/s burs-mode ransmission. In order o realize 10-Gb/s TDM-PON sysems, research on 10-Gb/s burs-mode ransmiers [68, 71 73], receivers [69, 74 84], and clock and daa recovery (CDR) [86 88] have been pursued. Furhermore, in recen years, 40-Gb/s capable NG-PON2 has been energeically discussed in he full service access nework (FSAN) [41]. As a resul of his discussion, hybrid TDM and WDM PON (TWDM-PON) sysems, which are realized by 4 wavelengh channels muliplexed for boh upsream and downsream, will be sandardized as an NG-PON2 [51, 52, 90]. The reason he TWDM-PON is seleced as he NG-PON2 is ha TWDM-PON is more cos-effecive compared wih oher proposed mehods such as high-speed TDM, orhogonal frequency division muliplexing (OFDM), and so on. On he oher hand, several approaches, including high-speed TDM, dense WDM (DWDM), OCDM, and OFDM, have been proposed o realize a capaciy larger han 40-Gb/s ha is more flexible and enables higher funcionaliy of opical access neworks. These high-capaciy neworks are called NG-PON3. NG-PON1 is required for he coexisence wih he curren 1-Gb/s TDM-PON ha has been widely insalled. In addiion, nework operaors require ha NG-PON2 preferably suppor operaion over legacy power splier-based PONs and possibly aggregae several such legacy PONs in order o reduce oal coss of building and operaing opical access neworks [49]. Moreover, long-reach ransmission longer han 40 km and a high spliing raio of more han 64 are required for NG-PON2 o expand he coverage area. Especially, long-reach ransmission is srongly required because mero-access hybrid neworks can be cosly by aggregaing OLT equipmen wih a mero ring node. Now, sandardizaion aciviy for NG-PON3 by applying revoluionary echnologies has no ye sared because NG-PON2 has no been realized by revoluionary echnologies as originally envisioned bu by he evoluional echnologies of TWDM. However, he requiremens for NG-PON3 will be increased sooner or laer. For NG-PON3, here are wo poenial approaches in erms of opical disribuion nework (ODN) migraion. One is coexisence on he legacy ODN. The oher is a

1.3. Roadmap of Opical Access Nework 9 modified ODN, which means addiion o or modificaion of he ODN ouside he OLT sie. Coexisence on he same ODN is a preferable alernaive, bu here is lile wavelengh region available for NG-PON3. Therefore, high specral efficiency will be necessary for NG-PON3 in order o coexis wih legacy neworks. OCDMA has unique characerisics capable of muliplexing a number of channels on a single wavelengh and an idenical ime slo wih up o 40-Gb/s capaciy per channel. Especially, OCDMA wih muli-level phase shif keying (PSK) opical code heoreically realizes good specral efficiency. For example, 10G-OCDMA wih a 16-level PSK opical code can achieve 0.8 bi/s/hz when a 16-channel wih 12.5-GHz channel spacing is muliplexed wihin a 200-GHz bandwidh [67]. This specral efficiency, which is as high as curren long-haul WDM sysems, can be realized because 40-Gb/s differenial quadraure phase shif keying (DQPSK) WDM sysems wih a 50-GHz channel spacing have 0.8 bi/s/hz. Therefore, OCDMA is suiable for NG-PON3 because i can realize high specral efficiency in opical access neworks ha require muliple access echnologies. NG-PON3 High-speed TDM-PON Sysem capaciy G-PON NG-PON1 XG-PON 10G-EPON 10.3-Gb/s NG-PON2 TWDM-PON 40-Gb/s DWDM-PON OCDM-PON OFDM-PON 1G-EPON 1.25-Gb/s Modified ODN Coexisence on he same ODN ~2005 ~2010 ~2015 ~2020 Year Fig. 1.4: Roadmap of opical access nework echnologies.

10 Chaper 1. Inroducion 1.4 Purpose of This Sudy There are hree issues for realizing high-speed, high specral efficiency, long-reach opical access sysems. The firs is a 10-Gb/s burs-mode ransmier/receiver. In order o launch he NG-PON1, 10-Gb/s bus-mode ransceivers wih a fas burs-mode response ime, a high power budge, and a wide dynamic range are required. The second one is a hybrid TDM OCDM ransmission. In fuure opical access neworks following NG-PON2, hybrid muliplexing echnologies such as TWDM will become he mainsream because i will be difficul o realize high-speed, cos-effecive neworks by adoping only one access echnology. OCDMA has huge poenial o realize he high-speed and flexible opical access neworks described in he previous secion. Several hybrid OCDM WDM neworks have been sudied [19, 97], bu few OCDM TDM hybrid neworks have been repored due o he lack of a high-speed burs-mode ransceiver. Feasibiliy sudies of a 1-Gb/s TDM OCDM hybrid sysem have been repored, where an SSFBG encoder/decoder and a burs-mode receiver for 1G-EPON were used [42]. However, a TDM OCDM capable of more han 10-Gb/s has no been repored. The hird issue is a long reach ransmission o direcly connec an exising opical access nework o a mero nework. Recenly, a long-disance ransmission over a 100-km single mode fiber (SMF) wihou inline dispersion compensaion was achieved by ailoring he opical specrum of he encoded signal in an OCDMA-PON sysem [101]. However, here sill remains a long reach ransmission of 10-Gb/s burs-mode opical code signal wihou dispersion compensaion. In his hesis, we sudy a 10-Gb/s burs-mode ransmier and receiver for realizing a 10-Gb/s TDM-PON sysem. In addiion, we propose a 10-Gb/s TDM OCDM hybrid PON sysem (10G-TDM-OCDM-PON) and invesigae long reach 10G-TDM-OCDM-PON sysems ha can realize direc connecions beween mero and access neworks. 1.5 Overview of he Disseraion Figure 1.5 shows he organizaion of his hesis. Following he inroducion of opical encoding and decoding schemes in OCDM neworks in Chaper 2, 10-Gb/s burs-mode ransmier and receiver echniques are described in Chaper 3. The 10G-TDM-OCDM-PON and long reach 10G-TDM-OCDM-PON sysems are proposed in Chapers 4 and 5, respecively. The conens of

1.5. Overview of he Disseraion 11 Chaper 1: Inroducion Chaper 2: Overview of opical code division muliplexing Chaper 3: 10-Gb/s burs-mode ransmission echnologies [II-1, II-6, III-1, III-4, III-5] Chaper 4: 10G-TDM-OCDM-PON sysem [I-1, II-2, II-3, II-4, III-2, III-3] Chaper 5: Long reach 10G-TDM-OCDM-PON sysem [I-2, II-5, III-6] Chaper 6: Conclusion Fig. 1.5: Organizaion of he hesis. each chaper are summarized as follows. Chaper 2 describes he opical encoding and decoding echniques. The fundamenals of he opical encoding and decoding schemes adoping a planer lighwave circui (PLC), an FBG, and an AWG are inroduced in his chaper. Then, we inroduce he properies of a muli-por encoder/decoder for a PSK opical code (OC). This muli-por encoder/decoder is suiable for our proposed long reach 10G-TDM-OCDM-PON sysems because i can process several OCs a he same ime. In Chaper 3, he 10-Gb/s burs-mode ransmier and receiver are described. Firs, we show he block diagram and opical performances of he 10-Gb/s burs-mode ransmier. In order o realize fas urn-on/off ime, a laser driver and a disribued feedback laser diode (DFB-LD) are conneced by an impedance conrolled DC coupling ransmission line. Second, he configuraion and performances of he 10-Gb/s burs-mode receiver are described. The 10-Gb/s burs-mode receiver can deliver a fas receiver seling ime and a wide dynamic range by adoping coninuous auomaic gain conrol (AGC) and auomaic hreshold conrol (ATC) for a ransimpedance amplifier and a limiing amplifier. The configuraion of he dual-rae receiver, which can be realized by swiching is ransimpedance gain and equivalen noise bandwidh, is also described. The resuls described in Chaper 3 have been published in II-1, II-6, III-1, III-4, and III-5 ha are shown in he lis of publicaions by he auhor.

12 Chaper 1. Inroducion In Chaper 4, we propose a 10G-TDM-OCDM-PON sysem ha muliplexes 10-Gb/s TDM-PON sysems by using OCDMA echniques. The proposed sysem is able o increase he oal capaciy wihou sacrificing he uplink bandwidh currenly assigned o each ONU. A 16-ONU (4-OCDMA 4-packe) uplink burs ransmission is experimenally demonsraed by using a hybrid 16-chip (200 Gchip/s), 16-phase-shifed SSFBG encoder/muli-por decoder and a burs-mode receiver along wih forward error correcion (FEC). Finally, we discuss how he newly inroduced muli-level phase-shifed encoding/decoding, wih which auo-correlaion waveform can be preferably adoped in he burs-mode recepion a 10-Gb/s, is he key o he proposed sysem. The resuls described in Chaper 4 have been published in I-1, II-2, II-3, II-4, III-2, and III-3 ha are shown in he lis of publicaions by he auhor. In Chaper 5, we propose a long reach 10G-TDM-OCDM-PON archiecure using only a muli-por encoder/decoder pair a an OLT and a remoe node (RN), which eliminaes he need for an encoder/decoder a each ONU. The 10G-TDM-OCDM-PON can be scaled up by aggregaing 10-Gb/s TDM-PON sysems wih OCDMA echniques. In addiion, a narrow band opical band pass filer (NB-OBPF) enables a long reach ransmission of 10G-TDM-OCDM-PON sysems wihou dispersion compensaion by ailoring he opical specrum. In he long reach 10G-TDM-OCDM-PON sysem, full duplex 4-packe 4-OC ransmission on a single wavelengh over a 65-km SMF wihou dispersion compensaor is demonsraed by using a 16 16 muli-por encoder and decoder, an NB-OBPF, and a 10-Gb/s burs-mode 3R receiver. We also discuss he sources of power penaly in he proposed long reach 10G-TDM-OCDM-PON sysem. The resuls described in Chaper 5 have been published in I-2, II-5, and III-6 ha are shown in he lis of publicaions by he auhor. Chaper 6 concludes he disseraion wih a summary of he overall resuls.

Chaper 2 Overview of Opical Code Division Muliplexing 2.1 Inroducion This chaper inroduces he OCDM echnologies, including opical encoding and decoding, on which he long reach 10G-TDM-OCDM-PON sysem proposed in his hesis are based. In Secion 2.2, fundamenal mechanisms of an opical encoding and decoding are described. There are several approaches o encode opical plain daa in ime and/or wavelengh domains. Secion 2.2 focuses on a ime domain coheren decoding scheme ha can deliver beer correlaion performances han oher schemes. Secion 2.3 describes he configuraion of opical devices for opical encoding/decoding including opical delay lines, a planar lighwave circui (PLC), a fiber Bragg graing (FBG), and an arrayed waveguide graing (AWG). In paricular, he opical encoder/decoder wih an AWG configuraion, called a muli-por encoder/decoder, has remarkable characerisics ha can process several opical codes simulaneously. Secion 2.4 shows he deails of he muli-por encoder/decoder configuraion and correlaion performances [67]. 13

14 Chaper 2. Overview of Opical Code Division Muliplexing 2.2 Principle of Opical Encoding/Decoding 2.2.1 Opical Encoding An opical encoding operaion opically ransforms each daa bi ino an opical code before ransmission. Opical encoding involves ranslaing a daa bi by a code sequence eiher in he ime domain or he wavelengh domain, or in a combinaion of he wo called wo-dimensional coding (2D-coding) [54]. Figure 2.1 shows an illusraion of hese classificaions. T (bi duraion) Plain daa 0 1 0 Time domain coding Incoheren 1 0 1 1 0 0 1 0 1 1 Coheren 0 0 0 0 0 0 Code Code Tc (chip duraion) Code 1 Wavelengh domain coding 2 6 10 2D coding 1 2 4 10 8 6 3 5 9 7 Tc (chip duraion) Code Fig. 2.1: Classificaion of differen opical encoding schemes.

2.2. Principle of Opical Encoding/Decoding 15 In a ime-domain opical encoded signal, each bi is spli ino ime componens shorer han he original bi slo, called chips. This ype of ime-domain opical encoding scheme can be classified ino wo caegories: an incoheren scheme [36, 37] and a coheren scheme [55]. In he ime-domain incoheren opical encoding scheme, he opical inensiy is manipulaed bu he phase is no. In conras, in he ime-domain coheren opical encoding scheme, he phase of he opical signal is manipulaed. The benefi of he incoheren scheme is ha i can be realized by an incoheren ligh source. However, he correlaion propery of he incoheren scheme is poorer han ha of he coheren one because of is unipolar characerisic. In he wavelengh-domain opical encoding signal, one encoded signal consiss of a unique subse of wavelenghs forming he code. The encoding process is based on Fourier ransform and does no require he high-speed opical modulaors used in ime-domain encoding sysems. 2D-coding combines he above ime-domain chip spreading and wavelengh selecion. One daa bi is encoded as consecuive chips of differen wavelenghs, forming a unique wavelengh sequence in ime consiuing one opical code. 2.2.2 Opical Decoding A a receiver, an opical decoding operaion reverse o he encoding process is performed o recover he original daa in he opical domain. Figure 2.2 shows an example of opical decoding for a ime-domain coheren binary phase shif keying (BPSK) code. The ransmied signal is encoded by an 8-chip BPSK signal as (,,,, 0, 0, 0, 0). There are wo opical decoders, o which differen opical code sequences are assigned, a he receiver. The opical decoder, o which he same opical code sequence of an incoming signal is assigned, oupus he auo-correlaion, which has a large peak in he cener of he oupu waveform (as shown in Fig. 2.2(a)) because of he exac maching of an incoming code sequence. The oher opical decoder, o which a differen opical code sequence such as (,, 0, 0,,, 0, 0) is assigned, oupus he cross-correlaion, which has no large peak [55] (as shown in Fig. 2.2(b)). Noe ha he cross-correlaion oupu does no vanish perfecly. This unwaned signal appears as noise in he decoder oupu, which is called muliple access inerference (MAI) noise. MAI is he principal source of noise in OCDM sysems. The larger he number of muliplexed opical codes used, he larger he MAI noise oupu. This MAI noise degrades he performance of OCDM sysems. In order o suppress i, opical hresholding [56] and/or opical ime gaing [57] have been proposed. These approaches can improve he sysem performance, bu i is cosly o inroduce opical hresholding devices, and

16 Chaper 2. Overview of Opical Code Division Muliplexing opical ime gaing limis he asynchronous operaion. I is imporan for an OCDM nework o choose a proper code having a good correlaion performance. Several opical codes, such as M sequence and gold codes, have been proposed o mee such requiremens [19]. Code lengh is also an imporan facor in sysem design, because a longer code lengh delivers a good correlaion propery, whereas he bi rae of plan daa is limied by he produc of he code lengh and he chip duraion. Incoming opical code (8-chip BPSK signal) (a) Auo-correlaion (b) Cross-correlaion Fig. 2.2: Auo-correlaion and cross-correlaion oupu of ime-domain coheren opical code. 2.3 Opical Devices for Opical Encoding/Decoding Figure 2.3 shows several approaches for opical encoding and decoding [58 66]. In a scheme ha demonsraed OCDMA for he firs ime, an inpu laser pulse is spli ino a se of delay lines in order o realize incoheren opical orhogonal codes (OOCs), as shown in Fig. 2.3(a). To passively generae an OOC, a bank of delay lines is placed beween a splier and a combiner. The combinaion of delay lines deermines he opical code srain. A he receiver side, received signals are decoded in he elecric domain, where a suiable clock recovery circui is required [59]. Figure

2.3. Opical Devices for Opical Encoding/Decoding 17 2.3(b) shows he configuraion of he specral encoding echnique using opical graings, lenses, and a phase or ampliude mask [60, 61]. The phase or ampliude mask is placed in he Fourier plane o imprin a code sequence ono he spaial frequency specrum. The signal is hen refleced by he second diffracion graing o recombine he specrum ino one spaial mode, which is coupled ino a fiber. The decoding process is reciprocal o he encoding scheme. For a ime-domain coheren opical code, a PLC device consising of unable aps and hermo-conrolled opical phase shifers has been proposed, as shown in Fig. 2.3(c) [62]. The phase shifer is an opical waveguide parly covered wih a heaer elecrode. The opical carrier phase can be varied by changing he emperaure of he waveguide ha changes he waveguide refracive index. In his opical encoding, an inpu single pulse is duplicaed o a se of chip pulses wih an idenical ampliude, and he opical carrier of each chip pulse is phase-shifed o eiher 0 or by phase shifers. Then, he chip pulses are recombined by an opical combiner o form a bipolar signaure code. In opical decoding, he same procedure as ha in he encoding is performed for all incoming opical code sequences. This archiecure has several benefis in erms of unabiliy and conrollabiliy for changing an opical code sequence. However, i does have some drawbacks, such as polarizaion dependency and he impossibiliy of realizing long code sequences due o consrains in device fabricaion. Figure 2.3(d) shows he block diagram of an opical encoder wih an FBG [63 65]. The FBG can easily generae a PSK opical code longer han he above PLC encoder can due o is low inserion loss. Acually, a long 511-chip 640-Gchip/s signal coded by a super-srucured FBG (SSFBG) has been repored [66]. This long PSK code can realize a 10-user ruly asynchronous 1.25-Gb/s coheren OCDMA nework. Figure 2.4 shows a SSFBG configuraion and an OC generaion scheme [64]. A SSFBG is defined as an FBG wih a slowly varying refracive-index modulaion profile imposed along is lengh [100]. In addiion, a complex refracive-index modulaion profile can be realized in an SSFBG by insering phase shifs beween differen segmens, as shown in Fig. 2.4(a). The inpu opical shor pulse can penerae he whole graing lengh, and he individual segmens of he graing conribue more or less equally o he refleced response when he lenghs of all segmens are all he same as L chip and he refracive-index modulaion is consan along he whole graing. The phase-shifed SSFBG hus works as an opical ransversal filer o generae a PSK OC from is impulse response, and i can also perform correlaion for OC recogniion. Figure 2.4(b) shows he principles of BPSK OC generaion. This sor of phase-shifed SSFBG can be fabricaed wih a single shor phase mask of lengh L chip by coninuous graing wriing [100] or holographic echniques [65]. These echniques provide a high flexibiliy in producing differen long opical code. High-precision phase conrol can be achieved as well for PSK OCs.

18 Chaper 2. Overview of Opical Code Division Muliplexing inpu pulse delay line lens mask oupu 001001 splier combiner graing lens inpu pulse graing (a) A se of he delay lines for OOC (b) Graings, lenses, and a mask for frequency spread OC inpu pulse unable ap inpu pulse combiner phase shifer fiber Bragg graing (FBG) planar lighwave circui (PLC) (c) PLC for PSK OC (d) FBG for long lengh OC Fig. 2.3: Opical encoding/decoding devices. Phase shifs Chip number 1 2 3 4 N chip Inpu pulse L chip L chip Phase shifs z n T chip 0 Posiion wih graing z Oupu OC Phase and ampliude 1 1 1 1 1 1 (a) SSFBG configuraion (b) Working principle for BPSK OC generaion Fig. 2.4: SSFBG wih phase shifs for BPSK OC. Recenly, as described in he previous chaper, mos opical access neworks have been consruced in a PON configuraion, i.e., a poin-o-mulipoin nework. Therefore, i is desired o generae muliple opical codes by a single opical device, especially for OLT sides. A novel muli-por opical encoder/decoder was proposed by adoping an AWG configuraion, which is known as a wavelengh muliplexer/demuliplexer. Figure 2.5 shows he configuraion of his muli-por encoder/decoder and is operaion [67]. Here, he numbers of inpu and oupu pors are equal o N. An incoming opical shor pulse is inpu from an arbirary inpu por. N copies of he

2.3. Opical Devices for Opical Encoding/Decoding 19 inpu pulse are generaed in he inpu slab coupler. The opical pulses ravel hrough differen pahs in he graing, and hen he oupu slab coupler recombines hem o build N copies a he device oupus. Each PSK code is composed of N opical chips, and he differenial pah delay in he graing is se o be larger han he inpu pulse widh so ha chips in he OC do no overlap in ime. This muli-por encoder/decoder is able o measure he correlaion beween any pair of codes, simulaneously. In fac, if an OC is sen o he inpu por, an auo-correlaion peak (ACP) appears a one of oupu pors and low power cross-correlaion signals appear a he ohers, univocally deermining he incoming OC. Opical Code 1 Opical Code N (a) Opical encoding diagram Auo-correlaion Opical Code 1 (b) Opical decoding diagram Cross-correlaion Fig. 2.5: Muli-por encoder/decoder wih AWG configuraion.

20 Chaper 2. Overview of Opical Code Division Muliplexing 2.4 Muli-Por Encoder/Decoder 2.4.1 Configuraion of Muli-Por Encoder/Decoder The mechanism o build a se of OCs can be easily described by analyzing he AWG in he ime domain. Referring o Fig. 2.6 and he parameers lised in Table 2.1, he impulse response from inpu por i o oupu por k can be wrien as N 1 nsd L l L hik ( ) exp j (2l N 1)(sini sino) ns l 0 c i, k 0,1, N 1, (2.1) where j 1, δ() is he Dirac s dela funcion, L is he shores waveguide lengh, and θ i and θ o are he diffracion angles in he inpu and oupu slab couplers, respecively di do sin i (2i N 1), sino (2k N 1). (2.2) 2R 2R For he sake of simpliciy, L is assumed o be 0, as is value affecs a consan ime delay bu no he code generaion process. The chip inerval, i.e., he ime inerval beween wo consecuive pulses in each code, is n s L / c, which equals he inverse of he free specrum range (FSR) of an AWG muliplexer/demuliplexer, and he correlaion ime is given by parameers lised in Table 2.1, 5 ps. 1) (N. From he The exponenial erm in Eq. (2.1) corresponds o he phase of each chip in he code. We se di d o o, i.e., idenical spacing in he inpu and oupu graings. Equaion (2.1) can hen be reduced N 1 hik ( ) exp j (2l N 1)( i k 1) l l 0 N i, k 0,1, N 1. (2.3) The OCs are N-array PSK codes. For a given inpu por i, he code generaed a oupu por k N i 1 has all chips wih an idenical phase.

2.4. Muli-Por Encoder/Decoder 21 L+lL N-1 i N-1 R d i d 1 0 l o R d o 0 1 i 1 0 N-1 k Fig. 2.6: Muli-por encoder/decoder configuraion. Table 2.1: Parameers of muli-por encoder/decoder. Symbol Descripion Value Uni f 0 Carrier frequency ( = 1550.984 nm) 193.292 THz N Number of pors 16 R Inpu/oupu slabs focal lengh 20.85 mm d Spacing of waveguide array a he inpu/oupu slab couplers 24.6 m w g AWG waveguide widh 7 m d i Inpu waveguide spacing a he inpu slab coupler 56.47 m d o Oupu waveguide spacing a he oupu slab coupler 56.47 m w Waveguide widh in he inpu/oupu graing 50 m L Differenial pah lengh 1.0316 mm n s Effecive refracive index 1.468

22 Chaper 2. Overview of Opical Code Division Muliplexing 2.4.2 Correlaion Propery According o Parseval s heorem, he correlaion funcion beween wo OCs generaed a oupu pors k and k can be evaluaed in he frequency domain as h ik ( ) hik ' ( ) H ik ( f ) H ik ' ( f )exp( j 2f) d ' k, k 0,1, N 1, (2.4) where denoes he convoluion uni and H ik ( f ) is he ransfer funcion from he inpu por i o he oupu por k, obained by he Fourier ransform of Eq. (2.3) as H ik N 1 i k 1 ( f ) exp j (2l N 1) f l 0 N sin ( i k 1 Nf ) exp j ( N 1) f i k 1 sin f N i, k 0,1, N 1. (2.5) The power specra of oupu por k are ploed in Fig. 2.7. Two OCs are orhogonal when he cross-correlaion funcion of Eq. (2.4) vanishes everywhere, which happens when he wo corresponding ransfer funcions H ik ( f ) and ( f ) do no overlap wih each oher and heir H ik ' produc is zero. Therefore, Eq. (2.4) indicaes he code-recogniion capabiliy of a full encoder/decoder, and he lower he crossalk beween wo adjacen frequency channels, he more orhogonal he corresponding OCs. OCs generaed a wo adjacen oupus are less orhogonal since he crossalk beween wo adjacen frequency channels is higher han he ohers.

2.4. Muli-Por Encoder/Decoder 23 0-5 -10-15 -20-25 -30-35 -40 1550 1551.6 1550.4 1550.8 1551.2 Wavelengh (nm) H ik (f) 2 (db) Fig. 2.7: Transfer funcion a wo adjacen oupu pors. The correlaion signal is compued by subsiuing Eq. (2.3) ino Eq. (2.4) and performing simple algebra: ) ( ) ' ( ' 2 exp 1) ( 1) ( 2 exp ) ( ) ' ( ' 2 exp 1) ( 1) ( 2 exp ') ( 1) ' 1)( ' (2 exp 1) 1)( (2 exp ) ( ) ( 1 2 1 ' 2 2 0 ' 1 0 1 0 1 0 ' ' l k k N l k i N l l k k N l k i N l l l k i N l N k i N l N h h N l l N N l l l N l N l N l ik ik j j j j j j 1 0,1, ',, N k k i. (2.6) To evaluae he auo-correlaion funcion, k k ' is considered in Eq. (2.6):

Chaper 2. Overview of Opical Code Division Muliplexing 24 ) ( 1) (2 1) ( 1) ( 2 exp ) ( 1) ( 1) ( 1) ( 2 exp ) ( ) ( 2 2 1 0 l l N k i N l l l k i N l h h N N l N l ik ik j j 1 0,1,, N k i, (2.7) and he ACP appears a ) 1 (N as N h h ACP N ik ik 1) ( ) ( ) ( 1, 01,, N k i. (2.8) Furhermore, he maximum sidelobe (MSL) of he auocorrelaion funcion is ) ( 1 N MSL. In he case of k k ', he cross-correlaion funcion of Eq. (2.6) becomes ) ( ') ( sin ') 1)( ( sin 2 ' 1 1) ( 2 exp 2 ') ( exp ) ( ) ( 2 2 0 ' l N k k N k k l k k i N l N k k h h N l ik ik j j 1 0,1, ',, N k k i, (2.9) and he maximum CCP appears a 1 ) ' 2( / 1) 2 ( k k q wih N k k N q / ') 1)( 2(2,,1, 0, where denoes he ineger par, and is N k k h h CCP k k N ik ik ) ' ( sin 1 ) ( ) ( 1 ') ( 2 ' 1 0,1, ', N k k i. (2.10)

2.4. Muli-Por Encoder/Decoder 25 Figure 2.8(a) shows he inensiy and he phase of an OC generaed by a 4-ps widh Gaussian-shape pulse, and Fig. 2.8(b) shows is auo-correlaion funcion. Figures 2.8(c) and (d) show he cross-correlaion funcions beween OCs generaed a wo adjacen oupu pors and a wo far-apar pors, respecively. As shown in Fig. 2.8, he raio of APC and max CCP is enough o recognize auo-correlaion oupu. (a) Normalized inensiy (b) Normalized inensiy (c) Normalized inensiy (d) Normalized inensiy 1.0 0.5 0 0 10 20 30 40 50 60 70 80 90 100 Time (ps) 15 10 5 0 0 15 10 5 0 0 15 10 5 0 0 50 100 150 Time (ps) 50 100 150 Time (ps) 50 100 150 Time (ps) Phase ACP max CCP min CCP Fig. 2.8: (a) PSK code generaed by he device for an inpu 4-ps Gaussian-shape pulse. (b) Auo-correlaion waveform. (c) Maximum cross-correlaion waveform. (d) Minimum cross-correlaion waveform.

26 Chaper 2. Overview of Opical Code Division Muliplexing 2.5 Conclusion In his chaper, an overview of OCDM echnologies has been described. Secion 2.2 has described he fundamenals of opical encoding and decoding. We have shown ha a difference in he peak power beween auo- and cross-correlaion signals can disinguish a desired received signal from he ohers. We have also explained ha he oupu powers of cross-correlaion signals do no vanish, which leads o MAI noise. In Secion 2.3, opical devices for opical encoding/decoding have been discussed. Among several opical devices proposed o dae, a muli-por encoder/decoder wih an AWG configuraion is he mos suiable device for OCDMA sysems in PON archiecures. In Secion 2.4, he configuraion of a muli-por encoder/decoder and he properies of a PSK OC have been described. These devices and he OC echniques form he basis of our proposed sysem, which is described in he following chapers.

Chaper 3 10-Gb/s Burs-Mode Transmission Technologies 3.1 Inroducion In his chaper, he performances of a 10-Gb/s burs-mode ransmier for an ONU [68] and a 10-Gb/s burs-mode receiver for an OLT [69], boh for 10G-EPON sysems, are shown. The key issue for ONU and OLT ransceivers is a sufficien response ime o deal wih fas burs modes. Secion 3.2 describes he configuraion and performances of our 10-Gb/s burs-mode ransmier. In order o obain a fas response waveform in he ransmier, an impedance conrolled DC-coupled ransmission line is applied o he burs-mode ransmier in he ONUs. Secion 3.3 shows our 10-Gb/s burs-mode receiver configuraion and is performances. For smooh migraion from 1-Gb/s o 10-Gb/s access sysems, he OLT of he 10G-EPON mus be able o receive 10-Gb/s and 1-Gb/s packes. Dual-rae burs-mode auomaic gain conrol (AGC)/auomaic hreshold conrol (ATC) funcions are applied o our OLT receiver in order o ensure a wide dynamic range for dual-rae burs-mode opical signals. 27

28 Chaper 3. 10-Gb/s Burs-Mode Transmission Technologies 3.2 10-Gb/s Burs-Mode Transmier Technologies 3.2.1 10-Gb/s Burs-Mode Transmier Configuraion Figure 3.1 shows he block diagram of our 10-Gb/s burs-mode ransmier. I consiss of a burs-conrol circui, an LD driver, a bias circui, a feedforward auomaic power conrol (APC) circui, and a 1.27-m un-cooled DFB-LD suiable for 10-Gb/s direc modulaion. The burs conrol circui can generae 10.3-Gb/s burs daa based on boh exernal 10.3-Gb/s coninuous daa and burs gae signals. The LD driver is able o provide a modulaion curren (I mod ). The bias circui can supply a sable bias curren (I bias ) wih a rapid on/off ime. On/off swiching of he burs-mode curren is conrolled by a pre-bias signal. The LD modulaion curren and he bias curren are conrolled by he feedforward APC circui wih an elecrically erasable and programmable read-only memory (EEPROM) ha sores a lookup able of appropriae modulaions and bias currens for he enire emperaure range. In ypical coninuous-mode ransmiers, he opical oupu power is conrolled by monioring he monior phoo deecor (PD) curren, which is called a feedback APC. However, i is difficul o achieve a burs-mode fas response of modulaion and bias currens wih he feedback APC due o a slow response ime of he monior PD curren. In conras, in he feedforward APC, he modulaion and 10-Gb/s burs-mode ransmier 10.3-Gb/s daa Burs gae Burs conrol Impedance-conrolled DC-coupled line LD driver 1.27-m DFB-LD Opical oupu Pre-bias Bias circui I mod I bias Feedforward APC circui EEPROM Fig. 3.1: Block diagram of 10-Gb/s burs-mode ransmier.

3.2. 10-Gb/s Burs-Mode Transmier Technologies 29 bias currens are uniquely deermined based on he emperaure. Therefore, he feedforward APC circui is suiable for burs-mode operaion and can keep he oupu launch power and exincion raio consan over he full emperaure range. An impedance-conrolled DC-coupled ransmission line is insered beween he DFB-LD and he LD driver circui in he opical ransmier. The ransmission inerface beween he DFB-LD and he driver circuis includes an opimally designed RC nework and a flexible srip-line cable o compensae for he parasiic inducance of he opical module. In order o realize a DC-coupled ransmission line in he burs-mode ransmier, supply volages o he oupu sage of he LD driver and DFB-LD are se o be as high as 5.0 V and he supply volages o oher pars are 3.3 V o reduce he power consumpion. Wih he DC-coupled ransmission line, his impedance conrolled line enables boh high curren modulaion above 10.3-Gb/s and fas burs-mode conrol wihou ransmier waveform disorion. 3.2.2 Experimenal Resuls Figure 3.2 shows he measured urn-on, urn-off, and opical oupu eye waveforms afer he 4h-order 10.3-Gb/s Bessel-Thomson filer a case emperaures of Tc = 0, +25, and +75 C. The inpu daa paern was PRBS 2 31 1. In he measuremen, we applied a pre-bias burs-mode [40], and he urn-on ime represens he convergence ime o wihin 10% deviaion of he firs bi pulse-widh disorion induced by he urn-on delay of he direc modulaed DFB-LD and he ransien response of he driver circui. As shown in Fig. 3.2, a fas urn-on ime of less han 10 ns and a urn-off ime of 7 ns were achieved. In addiion, clear eye mask margins (MM) of up o 24% higher han he IEEE802.3av sandard [39] were obained. The measured average power and he exincion raio of he ransmier oupu are shown in Fig. 3.3. We confirmed ha a high average oupu power of more han +7.0 dbm and an exincion raio of 7.0 db, ogeher wih very small emperaure-dependen power and exincion raio deviaions of less han 0.1 db, were achieved over a wide emperaure range due o using he feedforward APC circui. These opical oupu power and exincion raios saisfy IEEE802.3av PR30 sandards over he full emperaure range.

30 Chaper 3. 10-Gb/s Burs-Mode Transmission Technologies Turn-on (5 ns/div) 10 ns Turn-off (5 ns/div) 7 ns Opical eye waveforms (20 ps/div) 0 o C MM=24% 10 ns 3 ns +25 o C MM=34% 10 ns 5 ns +75 o C MM=27% Fig. 3.2: Oupu waveforms of urn-on/off and opical eye waveforms. 10 10 Opical oupu power (dbm) 9 8 7 6 5 4 3 2 1 0 IEEE802.3av PR30 spec. 0 10 20 30 40 50 60 70 Exincion raio (db) 9 8 7 6 5 IEEE802.3av PR30 spec. 4 3 2 1 0 0 10 20 30 40 50 60 70 Case emperaure ( o C) Case emperaure ( o C) (a) Opical oupu power (b) Exincion raio Fig. 3.3: Opical oupu power and exincion raio of 10-Gb/s burs-mode ransmier.

3.2. 10-Gb/s Burs-Mode Transmier Technologies 31 3.2.3 Analysis of Burs-Mode Performances Figure 3.4 shows he measured and calculaed pulse-widh disorions versus pre-bias seing ime of Tc = +25 C. In his figure, he calculaed curve uses he rae equaions for he inrinsic ransien response of he direcly modulaed DFB-LD [70]. The rae equaions are as follows: dn d dp d I N GN ( N N 0 ) 1 P P, (3.1) q V a P N GN N N 0 1 P P, (3.2) ph s s where N is he carrier densiy, P is he phoon densiy, I is he injecion curren, q is he elemenary charge, V a is he volume of he acive region, is he phenomenological gain compression facor, s is he carrier lifeime, G N is he gain coefficien, is he opical confinemen facor, N 0 is he ransparen carrier densiy, ph is he phoon lifeime, and is he sponaneous emission coupling facor. I can be clearly seen in Fig. 3.4 ha our burs-mode ransmier can achieve a fas LD urn-on ime close o he inrinsic DFB-LD lifeime-dominaed ransien response because he pulse-widh disorion wih 3-ns pre-bias seing ime is less han 10%. The difference beween he measured and heoreical resuls can be explained by he circui delay due o inducance in he bias line. As shown in Fig. 3.4, a pre-bias seing ime of longer han 10 ns is suiable for a 10-Gb/s burs-mode ransmier o avoid pulse-widh disorions. 100 Pulse-widh disorion (%) 80 60 40 20 0 Measured daa Calculaed daa 10% 0 5 10 15 20 Pre-bias seing ime (ns) Fig. 3.4: Measured and calculaed pulse-widh disorions versus pre-bias seing ime.

32 Chaper 3. 10-Gb/s Burs-Mode Transmission Technologies 3.3 10-Gb/s Burs-Mode Receiver Technologies 3.3.1 Burs-Mode Receiver Configuraion In general, a burs-mode opical receiver consiss of an avalanche phoo diode (APD), a ransimpedance amplifier (TIA), and a limiing amplifier (LIA) incorporaing burs-mode AGC/ATC funcions. Burs-mode receivers can be caegorized roughly ino wo ypes: sep deecion and coninuous deecion [85]. Received burs opical packes have differen power levels, so each packe should be normalized by amplificaion wih an appropriae gain and regeneraion a a proper decision hreshold level in a burs-mode opical receiver, as shown in Fig. 3.5. The echnical challenge for burs-mode AGC/ATC is o simulaneously suppor quick response o incoming burs packes and high olerance o long consecuive idenical digis (CIDs). A burs-mode receiver of he sep deecion ses is gain o he highes mode before receiving a packe. Then, i deermines is gain and hreshold according o he received power a he beginning of an incoming packe. Wih hese operaions, a burs-mode receiver of he sep deecion ype [83, 84] can realize a receiver seling ime as fas as 51 ns as well as olerance o a long CID. However, he drawback is ha i needs a rese signal inpu a he leading edge of each packe a he righ momen. In conras, a burs-mode receiver of he coninuous deecion ype can vary is gain and hreshold coninuously according o he received power averaged over he ime. As a resul, a burs-mode receiver of he coninuous deecion ype [76, 81] can realize a simple configuraion and robusness agains power flucuaion in a packe. However, i is difficul o achieve a fas receiver seling ime shorer han 150 ns in order o reain sufficien srengh for a long CID. Therefore, we adop he coninuous deecion ype for he 10-Gb/s burs-mode receiver. APD TIA Peak deec ATC S/D LIA APD TIA Coninuous S/D ATC LIA Sep AGC Rese Peak deecor Rese - Weak agains power flucuaion - Rese needed - Very fas seling (a) Sep deecion Coninuous AGC Average deecor Average deecor - Srong agains power flucuaion - Rese free - No very fas (b) Coninuous deecion Fig. 3.5: Block diagrams of burs-mode receiver for TDM-PON.

3.3. 10-Gb/s Burs-Mode Receiver Technologies 33 3.3.2 Dual-Rae Receiver Configuraion In his secion, he dual-rae receiver configuraions ha have also been proposed are discussed. In 10G-EPON sysems, he upsream wavelengh regions of 10-Gb/s and 1-Gb/s sysems are overlapped from 1260 nm o 1280 nm. Therefore, an OLT receiver has o receive boh 10-Gb/s and 1-Gb/s packes. In order o mee such demand, here are hree main configuraions of a dual-rae receiver. Figures 3.6(a), (b), and (c) show he block diagrams of parallel (opical spliing [75] and TIA oupu spliing ypes [76]), and serial ypes of a dual-rae opical receiver for a 10G-EPON OLT, respecively. In he opical spliing ype, he received opical signal is divided by a 3-dB coupler and 10-Gb/s and 1-Gb/s signals are received by each daa rae receiver including an APD, a TIA, and a LIA. The advanage of his mehod is ha cos-effecive 1-Gb/s opical and elecrical componens for 1G-EPON can be applied. However, he receiver sensiiviy becomes worse han ha achieved by oher mehods due o he 3-dB coupler. In addiion, he number of componens in he receiver is large. The TIA oupu spliing ype can be realized by a single APD and 10-Gb/s TIA, as well as by parallelized 10-Gb/s LIA and 1-Gb/s LIA following a low-pass filer (LPF) wih a 1-GHz cuoff frequency. This ype can reduce he number of componens compared wih he opical spliing ype, bu he receiver sensiiviy for he 1-Gb/s signal is no opimized due o applying a 10-Gb/s TIA, which has a ransimpedance gain lower han ha of a 1-Gb/s TIA. The serial ype dual-rae receiver can realize opimized ransimpedance gain and equivalen noise bandwidh by changing he operaion mode wih an exernal rae selec signal. In addiion, he number of opical componens, he power consumpion, and he cos can be minimized. Therefore, we adop he serial ype for he dual-rae burs-mode receiver. APD 10-Gb/s TIA 10-Gb/s LIA APD 10-Gb/s TIA 10-Gb/s LIA APD 1/10-Gb/s TIA 1/10-Gb/s LIA APD 1-Gb/s TIA 1-Gb/s LIA 1-Gb/s LIA LPF Rae selec signal (a) Opical spliing ype (b) TIA oupu spliing ype (c) Serial ype Fig. 3.6: Block diagrams of parallel and serial ypes of dual-rae receiver for 10G-EPON OLT.

34 Chaper 3. 10-Gb/s Burs-Mode Transmission Technologies 3.3.3 Dual-Rae Burs-Mode Transceiver Configuraion Figure 3.7 shows he block diagram of a dual-rae opical ransceiver for a 10G-EPON OLT. I consiss of a dual-rae burs-mode opical receiver and 10-Gb/s and 1-Gb/s downsream ransmiers inegraed ino an XFP-E size package via a riplexer opical module [89]. The burs-mode opical receiver employs a dual-rae APD-preamplifier and a dual-rae limiing amplifier ha can swich heir ransimpedance gain, equivalen noise bandwidh, and ransien response ime opimized for each 10-Gb/s and 1-Gb/s packe in order o achieve he receiver sensiiviy and receiver seling ime specified in he IEEE802.3av PR30 sandards. These dual-rae preamplifier and limiing amplifier ICs are fabricaed by he 0.13-m SiGe BiCMOS process o realize single-core chip ses and low power consumpion. The APD bias conrol circui applies he opimized volage for he APD over he enire emperaure range in order o achieve a high receiver sensiiviy. The 10-Gb/s and 1-Gb/s ransmiers employ a cooled 10-Gb/s elecro-absorpion modulaor inegraed laser (EML), an un-cooled 1-Gb/s DFB-LD, and driver ICs o drive hese ligh sources. Fig. 3.7: Block diagram of dual-rae burs-mode ransceiver for 10G-EPON OLT.

3.3. 10-Gb/s Burs-Mode Receiver Technologies 35 3.3.4 Experimenal Resuls The measuremen resuls of our dual-rae burs-mode dynamic receiving response are shown in Fig. 3.8. In Fig. 3.8(a), he inpu signal consiss of 10-Gb/s opical sof packes wih an opical power of 30 dbm and 1-Gb/s loud packes wih 6 dbm wihou guard ime for he wors case condiion. In Fig. 3.8(b), he inpu signal consiss of 10-Gb/s packes wih a power level of 6 dbm and 1-Gb/s packes wih a power level of 35 dbm. Figure 3.8 clearly shows ha he dual-rae burs-mode AGC and ATC could rapidly regenerae he received 10-Gb/s and 1-Gb/s mixed packes wihin 800 ns for he 10-Gb/s packe and 400 ns for he 1-Gb/s packe, which are specified as he receiver seling ime in IEEE802.3av, over he enire dynamic range. Figure 3.9 shows all of he BER measuremen condiions in he 10-Gb/s and 1-Gb/s coexising 10G-EPON sysems. In he dual-rae 10G-EPON sysems, here are hree BER measuremen 10-Gb/s packe: -30 dbm 1-Gb/s packe: -6 dbm 1-Gb/s packe: -35 dbm 10-Gb/s packe: -6 dbm Opical inpu Rae selec signal Elecrical oupu 1-Gb/s packe: -6 dbm 10-Gb/s packe: -30 dbm Preamble (800 ns) 100 s/div 100 s/div Payload 10-Gb/s packe: -6 dbm Preamble (400 ns) 1-Gb/s packe: -35 dbm Payload Opical inpu Rae selec signal Elecrical oupu 100 ns/div 100 ns/div (a) 1-Gb/s loud and 10-Gb/s sof packes (b) 10-Gb/s loud and 1-Gb/s sof packes Fig. 3.8: Dual-rae burs-mode dynamic receiving response.

36 Chaper 3. 10-Gb/s Burs-Mode Transmission Technologies (a) 1s packe No opical packe 2nd packe BER measuremen packe (10-Gb/s or 1-Gb/s) (b) (c) 10-Gb/s loud packe (Pin = -6 dbm) 1-Gb/s loud packe (Pin = -6 dbm) BER measuremen packe (10-Gb/s or 1-Gb/s) BER measuremen packe (10-Gb/s or 1-Gb/s) Preamble 10-Gb/s: 800 ns 1-Gb/s: 400 ns Payload Fig. 3.9: The BER measuremen condiions on dual-rae 10G-EPON. condiions for each 10-Gb/s and 1-Gb/s opical burs packe in erms of he opical inpu power and he line-rae of he firs (previous) packe because he dual-rae burs-mode AGC and ATC have o regenerae a second (BER measuremen) packe during a preamble period under all of he firs packe condiions. We measured he BER of payload in a second packe o confirm he feasibiliy of he dual-rae burs-mode AGC and ATC. The preamble periods of 10-Gb/s and 1-Gb/s packes are 800 ns and 400 ns, respecively, which are specified as he receiver seling ime in IEEE802.3av. The guard ime of he firs loud packe wih 6 dbm and BER measuremen packe was se o 0 ns for he BER measuremen condiion wih he wides dynamic range. The 10-Gb/s and 1-Gb/s payload daa paerns were 64B/66B and PRBS 2 7 1, respecively. The BER performances of he dual-rae burs-mode receiver are shown in Fig. 3.10. A minimum receiver sensiiviy of 30.6 dbm and an overload of 5 dbm a BER = 10-3 for 10-Gb/s operaion and a minimum receiver sensiiviy of 34.6 dbm and an overload of 9 dbm a BER = 10-12 for 1-Gb/s operaion were achieved. The receiver sensiiviies in all he measuremen condiions saisfied he requiremens of IEEE802.3av PR30 wihin an appropriae margin. A 10-Gb/s cooled EML wih a wavelengh of 1577 nm conrolled by an APC circui was used for an OLT 10-Gb/s downsream ransmier. A high average oupu power larger han +2.6 dbm and an exincion raio higher han 8.9 db a he case emperaure range from 5 o 70 C, boh of which mee he IEEE802.3av PR30 sandards, were achieved. A measured 10-Gb/s ransmied opical

3.3. 10-Gb/s Burs-Mode Receiver Technologies 37 waveform afer a 4h-order Bessel-Thomson filer enabling a clear eye opening is shown in Fig. 3.11. In he 1-Gb/s downsream ransmier, a 1-Gb/s un-cooled DFB-LD wih a wavelengh of 1490 nm was used. The DFB-LD drive curren was conrolled by an APC conroller o compensae for he ransmier oupu power and he exincion raio over he enire emperaure range. A high average oupu power larger han +5.3 dbm and a high exincion raio larger han 14.3 db in he case of emperaures ranging from 5 o 70 C were obained, boh of which mee he IEEE802.3-2008/1000BASE-PX20 sandards. The measured 1-Gb/s ransmied opical waveform afer he 4h-order Bessel-Thomson filer enabling a clear eye opening is shown in Fig. 3.11. Bi error rae 10-2 10-3 10-4 10-5 10-6 10-7 10-8 10-9 10-10 10-11 10-12 10-13 IEEE802.3av PR30-28.0 dbm o -6.0 dbm 10-Gb/s BER (a) No opical packe (b) 10-Gb/s loud packe (c) 1-Gb/s loud packe 1-Gb/s BER (a) No opical packe (b) 10-Gb/s loud packe (c) 1-Gb/s loud packe IEEE802.3av PRX30-29.78 dbm o -9.38 dbm -45-40 -35-30 -25-20 -15-10 -5 0 Received opical power (dbm) Fig. 3.10: Dual-rae BER performance. 20 ps/div 200 ps/div (a) 10-Gb/s ransmier (b) 1-Gb/s ransmier Fig. 3.11: Oupu waveforms of (a) 10-Gb/s and (b) 1-Gb/s ransmiers.

38 Chaper 3. 10-Gb/s Burs-Mode Transmission Technologies 3.4 Conclusion In his chaper, we have described he performances of our ONU and OLT ransceivers for 10G-EPON sysems, including 10-Gb/s burs-mode ransmiing and dual-rae receiving echnologies. Table 3.1 shows he summary of he burs-mode ransmission performances including he ONU ransmier and he OLT ransceiver. The burs-mode ransmier for he ONU could achieve a fas burs-mode response ime shorer han 10 ns and a high launched opical power larger han +7.0 dbm. The OLT ransceiver could achieve high receiver sensiiviies of less han 30.6 dbm for 10-Gb/s packes and less han 34.6 dbm for 1-Gb/s packes, wih fas receiver seling imes of 800 ns for he 10-Gb/s packes and 400 ns for he 1-Gb/s packes. Table 3.1: Summary of burs-mode ransmission performances. ONU OLT Tx Tx Rx Descripion Wavelengh Average launch power Exincion raio Turn-on/off ime IEEE802.3 PR30 Resuls 1260 1280 1265 1273 4 9 7.01 7.02 > 6 7.03 < 512 < 10 Uni nm dbm db ns Descripion IEEE802.3 Resuls 10-Gb/s 1-Gb/s 10-Gb/s 1-Gb/s Uni Wavelengh 1575 1580 1480 1500 1578.5 1488 1495 nm Average launch power 2 5 2 7 2.6 3 5.3 5.4 dbm Exincion raio > 6 > 6 8.9 14.3 db Overload > 6.0 > 9.38 5 9 dbm Receiver sensiiviy < 28 < 29.78 30.6 34.6 dbm Receiver seling ime < 800 < 400 < 800 < 400 ns Burs dynamic range > 24 > 20.4 25.6 25.6 db

Chaper 4 10G-TDM-OCDM-PON Sysem 4.1 Inroducion In his chaper, we propose our novel 10G-TDM-OCDM-PON sysem ha can scale up convenional 10-Gb/s TDM-PON by aggregaing sysems using an OCDMA echnique. The proposed sysem is able o increase he oal capaciy wihou sacrificing he uplink bandwidh currenly assigned o he individual opical nework uni (ONU). Secion 4.2 presens he 10G-TDM-OCDM-PON sysem configuraion, which includes an ONU wih a compac super-srucured fiber Bragg graing (SSFBG) [99], an opical line erminal (OLT) wih a single muli-por encoder/decoder [67], and a 10-Gb/s burs-mode receiver [75]. Secion 4.3 describes a 16-ONU (4-OCDMA 4-packe) uplink burs ransmission experimen using 16-chip (200 Gchip/s), 16-phase-shifed OCs which generaions and recogniions were described in Chaper 2. In Secion 4.3, we discuss how he newly inroduced muli-level phase-shifed encoding/decoding, whose auo-correlaion waveform can be preferably adoped in he burs-mode recepion a 10-Gb/s, is he key o he proposed sysem and he uplink hroughpu performances. 39

40 Chaper 4. 10G-TDM-OCDM-PON Sysem 4.2 10G-TDM-OCDM-PON Sysem Configuraion Figure 4.1 shows he upgrade scenario of a single 10-Gb/s TDM-PON o n 10G-TDM-OCDM-PON sysems. When n convenional 10-Gb/s TDM-PON sysems including m ONUs are accommodaed, he bandwidh per user is reduced by a facor of n due o he naure of ime division muliple access (TDMA), resuling in he bandwidh reducion facor of m n, ha is, (10-Gb/s /m)/n per ONU. Here, he bandwidh means he daa rae for each user. In conras, he 10G-TDM-OCDM-PON sysem can mainain he bandwidh reducion facor of only he number of ONUs (= m) by assigning differen opical codes (OCs), OCs No. 1 n, o an individual 10-Gb/s TDM-PON sysem. For example, OC No. 1 is shared wih No. 1-1 1-m ONUs where uplink signals No.1-1 1-m in a group are ime-aligned wihou conenion. As a resul, he uplink bandwidh per user can be increased by a facor of n, compared wih TDM-based sysems, ha is, 10-Gb/s/m. From he viewpoin of he upgrade cos of 10-Gb/s TDM-PON sysems, our proposed sysem is more expensive because OCDMA-specific componens have o be addiionally implemened. OCDMA-specific componens addiional o convenional PON sysems would include an encoder/decoder as well as a special class of shor pulsed lasers. However, he coss of he muli-por decoder as well as ha of he shor pulsed laser can be shared by a number of differen ONUs, and he SSFBG ype of encoder could be inexpensive if i were mass-produced. For 10G-TDM-OCDM-PON sysems, a single muli-por encoder/decoder [67] is locaed a an OLT, which can generae n differen OCs, while each ONU uses a muli-level phase-shifed SSFBG. The muli-por encoder/decoder can lower he budge loss due o simulaneous processing of muliple OCs wihou spliers. I is also cos-effecive because he cos can be shared beween all ONUs. In conras, an SSFBG has he abiliy o process an ulra-long OC, perform polarizaion-independen operaion, has a compac srucure, and also has a low-cos capabiliy for mass producion [65]. Therefore, i is appropriae o allocae a muli-por encoder/decoder o he OLT and SSFBG encoder/decoders o he ONUs, respecively. A crucial challenge of 10G-TDM-OCDM-PON sysems is he deecion of uplink opical burs signals, decoded afer he ransmission. To sudy he feasibiliy of 10G-TDM-OCDM-PON sysems, we developed a 10-Gb/s burs-mode receiver consising of an avalanche phoodiode (APD)-preamplifier module and a limiing amplifier. This burs-mode receiver can achieve high sensiiviy by adoping a high-sensiiviy APD wih a large gain-bandwidh produc [91] and a low-noise preamplifier.

4.2. 10G-TDM-OCDM-PON Sysem Configuraion 41 10-Gb/s TDM-PON #1-1 ONU splier OLT #1 #1-1 ONU SSFBG Encoder/Decoder Code #1 OLT #1 #1-m #2-1 #2-m ONU ONU ONU OLT #2 Muliplexed by OCDMA #1-m #2-1 #2-m ONU ONU ONU Code #n Code #2 Code #1 Code #2 splier Muli-por Encoder/Decoder Code #1 OLT Code #2 #2 #n-1 ONU #n-1 ONU OLT #n OLT #n #n-m ONU #n-m ONU Code #n Code #n 1 2 m m-packe Uplink bandwidh per ime-slo = 10-Gb/s / m n-oc 1 2 m 1 1 2 2 m m m-packe Uplink bandwidh per ime-slo = (10-Gb/s / m) n OC Fig. 4.1: Archiecures of scalable 10-Gb/s TDM-PON sysem upgraded using OCDMA approach. 4.3 Burs-Mode Uplink Transmission Experimen Figure 4.2 shows he experimenal seup for he 16-ONU uplink burs-mode ransmission of our 10G-TDM-OCDM-PON sysem. 16 ONUs can be accommodaed by a 4-packe 10-Gb/s TDM-PON over 4-OC OCDMA. A 1.8-ps pulse rain was generaed by a mode-locked laser diode (MLLD), as shown in Fig. 4.3(a). The cener wavelengh was 1546 nm and he repeiion rae was 9.95328 GHz. The oupu from he MLLD was modulaed o 4 packes by opical burs-mode modulaors (BM Mod.) consruced by a LiNbO 3 (LN) inensiy modulaor and an acouso-opic modulaor (AOM) ha worked as a burs-mode gae swich (SW). The swiching speed and exincion raio of he burs-mode gae swich were abou 100 ns and over 40 db, respecively. Therefore, he opical burs-mode modulaors could simulaneously realize a fas burs urn-on/off ime and sufficien power suppression during idle periods. Figure 4.3(b) shows he LN inensiy modulaor oupu daa wih a 2 31 1 pseudo random bi sequence (PRBS). Each packe lengh was 64 s, which includes a 10-s overhead, as shown in Fig. 4.3(c). Figure 4.3(d) shows he packe paern, which had a guard

42 Chaper 4. 10G-TDM-OCDM-PON Sysem 1546 nm MLLD 16-ONU (b) (a) (c) PC LN Gae SW BM Mod. 1 BM Mod. 2 BM Mod. 3 BM Mod. 4 (d) #1 SSFBG Encoder #2 #3 User Adjus TDL ATT User Adjus User Adjus (e) #4 User Adjus 9.95328 GHz Daa (PRBS 2 31-1) & burs gae signal 10-Gb/s burs-mode receiver Burs-mode PPG/BERT (g) (f) OLT Muli-Por Decoder 4-OC 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 4-packe OC Limiing amp. APDpreamp. BM Rx 1 BM Rx 2 1 2 POL Opical Fiber BM Rx 3 3 BM Rx 4 4 Fig. 4.2: Experimenal seup of 16-ONU uplink ransmission of 10G-TDM-OCDM-PON. ime of 0 ns. This no-guard ime was se o cope wih he mos severe condiion for a fas response of he burs-mode receiver. The packes were encoded by 4 differen 16-chip, 16-phase-shifed SSFBGs. In he SSFBG encoder, he inpu opical pulse was ime-spread ino 16 pulses, called chip pulses, a 5-ps inervals. These chip pulses had relaive phase shif wih respec o each oher s codes. In erms of he design parameers of he SSFBG encoder, he cener wavelengh was 1546 nm, he chip lengh was ~ 0.52 mm, he oal lengh of he graing was 8.32 mm, and he 16 phase levels were generaed by shifing he chip graing. These encoded signals were ime-muliplexed ino a TDM OCDM signal. A unable opical aenuaor (ATT), a unable delay line (TDL), and a polarizaion conroller (PC) were insered in each pah o invesigae he sysem performance in he wors scenario where inerference would become he mos serious, as shown in Fig. 4.3(e). A he OLT side, he received signal was decoded by a 16-chip wih a 5-ps inerval (200 Gchip/s), 16-phase-shifed muli-por decoder ha could simulaneously process he 16 OCs. We se a PC and inline polarizer (POL) a he fron of he muli-por decoder due o he polarizaion dependence of he muli-por decoder. In he decoding process, each chip pulse was ime-spread again ino 16 pulses and experienced a relaive phase shif wih respec o he combinaion of he inpu and oupu

4.3. Burs-mode Uplink Transmission Experimen 43 pors. The frequency deviaion (channel spacing) beween neighboring pors of he 16 16 por decoder was 12.5 GHz. Figure 4.3(f) shows he decoded signal of OC No. 1, showing a high-peaked auo-correlaion waveform wih muliple access inerference (MAI) noise skirs. Each decoded signal was processed by our originally developed 10-Gb/s burs-mode receiver. This 10-Gb/s burs-mode receiver provides a high-sensiiviy burs-mode 2R funcion wih he opimal muliplicaion facor M of he APD (M = 8.0). Figure 4.3(g) shows a good elecrical eye opening obained from he decoded signal despie MAI noise hanks o he adequae bandwidh of he burs-mode receiver, which was wider han 6.0 GHz. In his experimen, erbium doped fiber amplifiers (EDFAs) were insered o compensae for he opical loss of each componen, such as he SSFBG encoders and he muli-por decoder. Figure 4.4 shows he measured bi error rae (BER) performances for all 16-ONU of he 4-OC 4-packe and hose of he back-o-back (B-o-B) non-encoded and non-decoded signals. All packes achieved error-free (BER < 10-3 ) operaion wih he FEC of Reed-Solomon (RS) (255, 223). In he 4-OC muliplexed sysem, a BER of less han 10-7 could no be measured due o MAI noise. However, he feasibiliy of he 10G-TDM-OCDM-PON sysem was clear because he 10-Gb/s TDM-PON sysem operaes wih a FEC. We obained good eye openings for all four decoded signals of OCs No. 1 4, as evidenced by he BER measuremens in Fig. 4.4. These resuls confirm an uplink bandwidh of 10-Gb/s/4, which is four imes larger han ha in convenional 10-Gb/s TDM-PON sysems, e.g., 10-Gb/s/16. Figure 4.5 shows he receiver sensiiviy a BER = 10-3 for all 16-ONU uplink daa. Receiver sensiiviy of less han 29.9 dbm was successfully achieved by adoping he high-sensiive burs-mode receiver, and he power penalies beween 4-OC 4-packe and back-o-back were less han 2.0 db and were caused by degradaion of opical signal-o-noise raio (OSNR) due o amplified sponaneous emission (ASE) from each EDFA and he MAI noise. A small deviaion in he receiver sensiiviies would be caused by he characerisic mismach of correlaion properies and he exincion raio of each packe. In his experimen, BER resuls by changing he received opical power of each packe and he lengh of guard ime are no shown due o he lack of a burs-mode opical amplifier [95]. However, he sysem feasibiliy was demonsraed by using he burs-mode receiver, which can process 10-Gb/s uplink packes wih differen opical power [75].

44 Chaper 4. 10G-TDM-OCDM-PON Sysem Packe lengh 64 s (a) MLLD oupu 50 ps/div 20 ps/div (b) LN inensiy modulaor oupu Packe paern #1 #2 #3 #4 (c) BM mod. oupu 30 s/div (d) Packe paern of 4 packes 30 s/div OC #1 ~ #4 (e) 4-OCDM 20 ps/div (f) Muli-por decoder oupu 20 ps/div (g) BM Rx oupu 20 ps/div Fig. 4.3: Waveforms of burs-mode OC ransmission signals.

4.3. Burs-mode Uplink Transmission Experimen 45-2 -2 OC #1-3 -4-4 -5-5 -6-6 -7-34 -32-30 -28-26 -24-22 -20-7 -34-18 -32 Received opical power (dbm) -2 OC #3 Log(BER) -26-24 -22-20 Received opical power (dbm) -20-18 OC #4 Packe #1 OC #4 Packe #2 OC #4 Packe #3 OC #4 Packe #4 Packe #1 (B-o-B) Packe #2 (B-o-B) Packe #3 (B-o-B) Packe #4 (B-o-B) -18-7 -34-32 -30-28 -26-24 -22 Received opical power (dbm) Fig. 4.4: Measured bi error rae performances of all 16 ONUs. -28-28 4-OC 4-packe -29-29 -22-4 -6-28 -24-3 -6-30 -26 OC #4-5 -32-28 -2 OC #3 Packe #1 OC #3 Packe #2 OC #3 Packe #3 OC #3 Packe #4 Packe #1 (B-o-B) Packe #2 (B-o-B) Packe #3 (B-o-B) Packe #4 (B-o-B) -5-7 -34-30 Received opical power (dbm) -4 Minimum Received Power (dbm) Receiver sensiiviy @ BER=10-3 (dbm) Log(BER) -3 OC #2 Packe #1 OC #2 Packe #2 OC #2 Packe #3 OC #2 Packe #4 Packe #1 (B-o-B) Packe #2 (B-o-B) Packe #3 (B-o-B) Packe #4 (B-o-B) OC #2 Log(BER) Log(BER) -3 OC #1 Packe #1 OC #1 Packe #2 OC #1 Packe #3 OC #1 Packe #4 Packe #1 (B-o-B) Packe #2 (B-o-B) Packe #3 (B-o-B) Packe #4 (B-o-B) Back-o-back -29.9 dbm -30-30 -31-31 -32-32 -33-33 -34-34 Packe: #1 #2 #3 #4 #1 #2 #3 #4 #1 #2 #3 #4 #1 #2 #3 #4 OC: #1 #1 #1 #1 #2 #2 #2 #2 #3 #3 #3 #3 #4 #4 #4 #4 Fig. 4.5: Measured receiver sensiiviy of all daa a BER = 10-3. -20-18

46 Chaper 4. 10G-TDM-OCDM-PON Sysem 4.4 Discussion 4.4.1 Correlaion Performances for 10-Gb/s Burs-Mode Recepion A burs-mode recepion is a mus for PON sysems and has never been realized a 10-Gb/s in any OCDMA sysem. This is because he auo-correlaion waveforms in opical decoding have a sharp peak, requiring ens of gigaherz bandwidh of he burs-mode receiver a 10-Gb/s. This requiremen can be me by narrowing he bandwidh of he decoded signal, and so his is he approach ha we have aken. Two differen phase-shifed encoding schemes for coheren TS-OCDMA have previously been proposed and demonsraed [93]. One is bipolar phase-shifed encoding (0, ) by using an SSFBG [65]. The oher is muli-level phase-shifed encoding by using a muli-por encoder/decoder [67]. Figures 4.6(a) and (b) compare he auo-correlaion waveforms of he bipolar and he 16-level phase-shifed encodings used in he ransmission experimens, respecively. The pulse widh of he auo-correlaion signal of he bipolar phase-shifed code (63 chips and 640 Gchip/s) is a few picoseconds wih side-lobe suppression while he envelope widh of he 16-level phase-shifed auo-correlaion signal is approximaely 80 ps (= 16 chip/200 Gchip/s). The difference in he pulse widh is he key o successful burs-mode recepion a 10-Gb/s. For 1G-TDM-OCDM-PON [42], he bipolar phase-shifed encoding has been adoped for he burs-mode recepion, bu his narrow pulse widh was a sumbling block a 10-Gb/s. This is because i is difficul o receive he bipolar phase-shifed auo-correlaion signal wihou OSNR degradaion, and a wide bandwidh receiver (ens of gigaherz) is required. Currenly, i is no feasible o achieve boh high-bandwidh and high-gain burs-mode recepion under he condiion ha he gain-bandwidh produc remains consan. In addiion, he bipolar phase-shifed encoding has anoher issue resuling from use of long OCs. The longer he code lengh becomes for a high bi rae, he narrower he auo-correlaion waveform because he chip pulse widh has o become narrower. This propery indicaes ha he bipolar phase-shifed encoding is inadequae for our proposed sysems. This is why we employed he muli-level phase-shif encoder, which provides a broad and smooh auo-correlaion emporal waveform. I is noeworhy ha he muli-level phase-shifed encoding can generae a larger number of codes han he bipolar phase-shifed encoding wih an idenical number of chips. Regarding iner-symbol inerference (ISI), he ISI noise has he same effec as he MAI and resuls in he power penaly in sysems [96]. The auo-correlaion pulse widhs of he 63-chip bipolar (640 Gchip/s) and he 16-chip muli-level (200 Gchip/s) are 200 and 160 ps, respecively. Therefore, he 16-chip muli-level phase-shifed code can reduce he influence of ISI more effecively han he

4.4. Discussion 47 (a) (b) 10 ps/div 20 ps/div Fig. 4.6: The auo-correlaion waveforms of (a) bipolar and (b) 16-level phase-shifed encoding. 63-chip bipolar code. In addiion, he muli-level phase-shifed code has a beer power conras raio (PCR) characerisic han he bipolar code [97]. I can suppress boh he coheren bea noise and he MAI noise. Therefore, he muli-level phase-shifed encoding is he bes soluion for 10G-TDM-OCDM-PON uplink burs ransmission because a burs-mode receiver wih a wide bandwidh is no required for processing he muli-level phase-shifed auo-correlaion signal. 4.4.2 Uplink Throughpu Performances The uplink performances of he proposed sysem are discussed in his subsecion. Figure 4.7 shows he uplink burs frame model discussed here. In a case in which he daa payload is fully loaded, uplink bandwidh per user can be wrien as BW GP m OH PMD 100 OH FEC n BR, (4.1) GP 100 m where BW is he bandwidh per user, BR is he bi rae of he sysem, GP is he gran period equal o he opical burs frame lengh, m is he number of ONUs belonging o a 10-Gb/s TDM-PON sysem, OH PMD is he PMD overhead consising of burs-mode urn-on/off and sync imes, OH FEC is he FEC overhead raio afer he FEC frame mapping, and n is he number of sysems muliplexed by using OCDMA echniques. Table 4.1 shows he parameer values assumed in calculaing he hroughpu of he proposed sysem. In his calculaion, we assume ha OH PMD includes he burs-mode CDR lock ime because burs-mode CDR can realize a quick burs-mode daa recovery [87]. In addiion, OH FEC

48 Chaper 4. 10G-TDM-OCDM-PON Sysem n-oc OH PMD OH FEC Daa payload OH PMD OH FEC Daa payload OH PMD OH FEC Daa payload OH PMD OH FEC Daa payload OH PMD OH FEC Daa payload OH PMD OH FEC Daa payload OH PMD OH FEC Daa payload OH PMD OH FEC Daa payload OH PMD OH FEC Daa payload OH PMD Daa payload OH PMD OH FEC Daa payload OH FEC Daa payload OH FEC OH PMD ONU #1 ONU #2 ONU #m OC GT GP Fig. 4.7: Uplink ransmission opical burs frame model. Table 4.1: Parameers of hroughpu calculaion. Quaniy Symbol Value Uni Bi rae BR 9.95328 Gb/s PMD overhead ime OH PMD 10 s FEC overhead OH FEC 12.9 % Guard ime GT 0 ns Gran period GP 1 ms Number of opical codes n 4 and GT are assumed o be 12.9% [94] and 1 ms, respecively. Oher parameers are se on he basis of he experimenal condiions. Figure 4.8 shows he calculaion resuls of he uplink bandwidh per user. Here, he number of users is n m. The uplink bandwidh per user of convenional 10-Gb/s TDM-PON sysems is given by Eq. (4.1) wih n = 1. The proposed sysem achieves a capaciy four imes larger han ha in convenional 10-Gb/s TDM-PON sysems. Therefore, an uplink bandwidh of 1 Gb/s per user is achieved even if he sysem accommodaes 32 users, and all users can use symmeric gigabi-bandwidh applicaions by applying OCDMA echniques. In addiion, he increase in nework capaciy by using OCDMA echniques can be adaped o addiional subscribers. For example, he number of users in his sysem can be increased o 128 wihou hroughpu degradaion, which is in conras o a 10-Gb/s TDM-PON sysem ha can only accommodae 32 users. The maximum number of users can be increased o more han 32 in he 10G-TDM-OCDM-PON sysem because he opical power raio beween he burs signal and he idle period is more han 40 db. According o he heoreical analysis of he maximum number in his coheren OCDMA sysem [98], provided ha encoding/decoding is properly performed, 32 users and more can be accommodaed a any bi rae, and he number of acive users depends on he coherency of he ligh source. As he coherence goes higher, he bea noise becomes more dominan han he MAI noise.

4.4. Discussion 49 The Uplink uplink bandwidh bandwidh per per user ONU(Gbps) (Gb/s) 10 1 0.1 10G-TDM-OCDM-PON Convenional 10-Gb/s TDM-PON Symmeric gigabi-bandwidh 0 16 32 48 64 80 96 112 128 The The number number of of ONUs users Muliplexing 4-OC Fig. 4.8: 10G-TDM-OCDM-PON uplink bandwidh calculaion resul. 4.5 Conclusion In his chaper, a novel 10G-TDM-OCDM-PON sysem ha does no sacrifice he currenly assigned uplink bandwidh per user has been described. The uplink burs-daa ransmission of 4 10-Gb/s TDM-PON sysems over 4 OC has been demonsraed by using a 16-chip (200 Gchip/s), 16-level phase-shifed SSFBG encoder a ONUs and a single muli-por decoder a an OLT. Wih he assisance of FEC, error-free operaion could be achieved in all 16 ONUs of he 10G-TDM-OCDM-PON, resuling in a oal capaciy four imes larger han he convenional 10-Gb/s TDM-PON. Finally, we have revealed ha he key o unprecedened symmeric uplink bandwidh is a newly inroduced 16-level phase-shifed encoding/decoding, of which an auo-correlaion waveform can be preferably adoped in a burs-mode recepion a 10-Gb/s. We have also showed ha 32 users can be accommodaed by being provided wih an up/down link of symmeric gigabi-bandwidh in 10G-TDM-OCDM-PON sysems.

Chaper 5 Long Reach 10G-TDM-OCDM-PON Sysem 5.1 Inroducion In his chaper, we propose a novel long reach 10G-TDM-OCDM-PON archiecure using only a muli-por encoder/decoder pair a an opical line erminal (OLT) and a remoe node (RN), hus eliminaing he need for an encoder/decoder a each opical nework uni (ONU) [103]. This long reach 10G-TDM-OCDM-PON can realize cos-effecive configuraion by removing he dispersion compensaor for long reach ransmission. Secion 5.1 shows he general archiecure of he long reach 10G-TDM-OCDM-PON. The hree key devices required for long reach ransmission wihou dispersion compensaion a single muli-por encoder/decoder pair, a narrow band opical band pass filer (NB-OBPF), and a 10-Gb/s burs-mode 3R receiver are described. In secion 5.2, an experimenal demonsraion of full duplex 4-packe 4-OC ransmission on a single wavelengh over a 65-km SMF wihou dispersion compensaor is described. In secion 5.3, we discuss he sources of he power penaly in he proposed sysem [104]. 51

52 Chaper 5. Long Reach 10G-TDM-OCDM-PON Sysem 5.2 Long Reach 10G-TDM-OCDM-PON Sysem Configuraion Figure 5.1 shows he general archiecure of he long reach 10G-TDM-OCDM-PON, which can be scaled up by aggregaing 10-Gb/s TDM-PON sysems wih he OCDMA echnique. We realize our long reach 10G-TDM-OCDMA-PON, m n -ONU (m-tdm packe n-ocdma), by eliminaing he need for an encoder/decoder a each ONU and dispersion compensaor. Insead, only he NB-OBPF and he muli-por encoder/decoder are inroduced a boh he OLT and he RN. Thus, a dispersion compensaion-free long reach can be realized by narrowly ailoring he opical code (OC) specrum. In downlink, each 10.3-Gb/s piece of daa is encoded by he muli-por encoder o aggregae 10-Gb/s TDM-PON downlink signals. The OC specrum is ailored by using NB-OBPF o miigae he chromaic dispersion effec. Therefore, encoded signals can be ransmied over a runk span and decoded a he RN. Furhermore, each decoded signal is ransmied over an access span and received by each ONU, while in uplink, 10.3-Gb/s burs daa from each ONU is muliplexed as TDM signals and ransmied over an access span. Then, uplink m-tdm signals are encoded wih differen OCs, followed by ailoring heir specra a he RN. Afer he runk span ransmission, uplink signals are decoded and recovered a he OLT. As a resul, he proposed sysem is able o gaher cenral offices and direcly connec o he mero/core neworks, leading o a cos-effecive, high-capaciy 10-Gb/s TDM-PON. The hree key echnologies for long reach 10G-TDM-OCDM-PON a single muli-por encoder/decoder pair, an NB-OBPF, and a 10-Gb/s burs-mode 3R receiver will be inroduced in he nex secion. #1 #2 #n OLT OLT OLT Muli-por en/decoder n-oc 10.3-Gb/s daa OLT #n OLT #1 OLT #1 NB-OBPF for downlink n-oc OC Trunk span 10.3-Gb/s burs daa OC 1 2 m 1 2 m 1 2 m m-packe NB-OBPF for uplink Remoe node Muli-por en/decoder Access span OLT #1 1 2 m ONU ONU ONU ONU ONU ONU #1-1 #1-m #2-1 #2-m #n-1 #n-m Fig. 5.1: The archiecure of long reach 10G-TDM-OCDM-PON.

5.2. Long Reach 10G-TDM-OCDM-PON Sysem Configuraion 53 5.2.1 Muli-Por Encoder/Decoder Pair a OLT and RN We applied a 16-chip wih 5-ps inerval (200 Gchip/s), 16-phase-shifed muli-por encoder/decoder pair, which can simulaneously process he 16 OCs, in he 10G-TDM-OCDM-PON. The inserion loss of his muli-por encoder/decoder is abou 10 db. This inserion loss migh be smaller by eliminaing device mismaches such as coupling loss because he inserion loss of a ypical AWG achieves only a few db. An opical amplifier is insered a an inpu por in order o compensae for he inserion loss. From he inserion loss poin of view, he muli-por encoder/decoder can increase he number of pors o more han 16. However, we only applied a 16 16 por encoder/decoder pair because we prepared only his one device for he experimen. In addiion, a hermal conroller for he muli-por encoder/decoder, whose conrol accuracy was less han 0.1 C, is necessary o obain good correlaion performances. In order o use his muli-por encoder/decoder for an oudoor componen, ahermal echnologies which are adoped for a par of AWG will be required. By using jus an encoder/decoder pair a an OLT and an RN, long reach 10G-TDM-OCDM-PON can be scaled up by aggregaion wih 10-Gb/s TDM-PON sysems. The configuraion of ONU becomes simpler han he 10G-TDM-OCDM-PON by eliminaing he need for an encoder/decoder a each ONU, as shown in Fig. 5.1. Noe ha he muli-por encoder/decoder can be locaed anywhere on he SMF ransmission line beween he OLT and ONUs because he nonlinear effec is negligible. As a resul, our proposed sysem is able o gaher cenral offices and direcly connec o mero/core neworks, leading o a cos-effecive high-capaciy 10-Gb/s TDM-PON. 5.2.2 Exended Reach by NB-OBPF For realizing long-reach ransmission of OC signals wihou dispersion compensaion, he NB-OBPF can ailor he OCs specrum. In convenional OCDMA sysems, he encoded signals canno be ransmied more han a few km on he SMF wihou dispersion compensaion because he specral widh of a non-filered OC is abou 3 nm due o applying an opical shor pulse source. However, N. Kaaoka e al. proposed 10-Gb/s OCDMA sysems capable of SMF ransmission wihou dispersion compensaion by ailoring he exra specrum componens of he OC [53]. Figure 5.2 shows he ideal principle operaion of ailoring OC specrum componens produced by he 16 16 por encoder/decoder. This encoder/decoder has he free specral range (FSR) of 200 GHz, which is nearly equal o 1.6 nm a 1550 nm. Noe ha he oupu wavelengh componen of he

54 Chaper 5. Long Reach 10G-TDM-OCDM-PON Sysem muli-por encoder/decoder has a cyclic naure due o he AWG configuraion, as shown in Fig. 5.2. Here, only one FSR componen filered by NB-OBPF can keep he signal informaion and decrease he effec of chromaic dispersion. Figure 5.3 shows he wavelengh response of he recangular shaped NB-OBPF. The bandwidh of NB-OBPF is se o he FSR of he muli-por encoder/decoder in order o ailor he OCs specrum. The ailored specrum has a bandwidh of jus 1.6 nm ha can be obained by adaping a recangular shaped NB-OBPF. As a resul, he NB-OBPF oupu specrum includes only 4-OC componens. If he bandwidh of NB-OBPF is larger han FSR, he received opical signal o noise raio (OSNR) is decreased because of he chromaic dispersion [53]. On he oher hand, if he bandwidh of NB-OBPF is narrower han FSR, he correlaion performance degradaion occurs because each OC can keep he orhogonal relaion. Figure 5.4 shows he 10.3-Gb/s decoded opical eye diagrams of one OC funcioning as 4 muliplexing OCs whose specra are ailored by he NB-OBPF. The back-o-back decoded eye diagram wih a muliple access inerference (MAI) noise skir can achieve a clear eye opening because of he excellen correlaion characerisic of he muli-por encoder/decoder and adequae specrum ailoring, as shown in Fig. 5.4(a). Figure 5.4(b) shows he decoded opical eye diagram afer 65-km ransmission of SMF as 4 OCs muliplexing. This eye diagram has more iner-symbol inerference (ISI) compared wih he back-o-back one due o he chromaic dispersion. However, he receiver can process he ransmied signal because he decoded OC signal can obain a sufficien eye opening. This demonsraes ha he combinaion of a muli-por encoder/decoder and NB-OBPF can achieve over 65-km ransmission on SMF wihou dispersion compensaion. 1.6 nm (FSR) Same OC informaion due o he AWG configuraion NB-OBPF cus specrum componens for ailoring OC Fig. 5.2: Ideal operaion principle of ailoring OC by 16 16 por encoder.

5.2. Long Reach 10G-TDM-OCDM-PON Sysem Configuraion 55 0 Power (db) -5-10 -15 1549.5 1.5495 1550.0 1.55 1550.5 1.5505 1551.0 1.551 1551.5 1.5515 1552.0 1.552 Wavelengh (nm) Fig. 5.3: Wavelengh response of he recangular shaped NB-OBPF. 20 ps/div 20 ps/div (a) Back-o-back (b) 65-km SMF ransmission Fig. 5.4: Decoded opical eye diagrams as 4 muliplexing OCs whose specra are ailored by he NB-OBPF. 5.2.3 10-Gb/s Burs-Mode 3R Receiver 10-Gb/s burs-mode receiving echniques are one of he mos crucial challenges afer long-reach ransmission wihou dispersion compensaion. Due o he degradaion of OSNR afer long-reach ransmission, i is necessary for he OLT receiver o have boh good receiver sensiiviy and high pulse widh disorion olerance. In order o sudy he feasibiliy of he 10G-TDM-OCDM-PON sysems, we developed he 10-Gb/s burs-mode 3R receiver incorporaing a burs-mode auomaic gain conrol (AGC) opical receiver and an 82.5 Gsample/s (8 10.3125 GHz) over-sampling

56 Chaper 5. Long Reach 10G-TDM-OCDM-PON Sysem burs-mode CDR o fully comply wih IEEE802.3av 10G-EPON PR30 sandards [78]. Figure 5.5 shows he block diagram of he 10-Gb/s burs-mode 3R receiver. The 10-Gb/s burs-mode 3R receiver is consruced by an APD-preamplifier IC, a limiing amplifier IC, and an 82.5 Gsample/s sampling CDR [87]. The funcion of he burs-mode AGC/ATC receiver has been described in Chaper 3. The 82.5 GSample/s over-sampling CDR produces eigh 10.3-GHz muli-phase clocks. These eigh clocks are sequenially shifed by 45 degrees per phase. Thus, incoming daa can be successfully capured by he sampling IC a he sampling resoluion of a high 12-ps, which is equal o 45 in phase a 10.3-Gb/s. This very high speed sampling resoluion can elevae he pulse-widh disorion olerance of he oversampling based CDR [21] because i can sample a very narrow eye opening region of daa. The incoming burs-mode daa can be reimed by selecing he adequae phase a an 82.5 GSample/s equivalen rae by eigh 45 phase-shifed clocks. The burs-mode receiver can realize high sensiiviy as well as a fas response by adaping in combinaion wih he burs-mode AGC, ATC, and 82.5 GSample/s over-sampling echniques. APD Preamplifier IC Limiing amplifier IC Sampling CDR 82.5 Gsample/s sampling AGC ATC 10.3 GHz 8 phase PLL Selecing adequae phase oupu Sysem CLK Fig. 5.5: Block diagram of 10-Gb/s burs-mode 3R receiver.

5.3. Full-Dulplex Transmission Experimen wihou Dispersion Compensaion 57 5.3 Full-Duplex Transmission Experimen wihou Dispersion Compensaion 5.3.1 Experimenal Seup and Transmission Performance The ransmission performances of our proposed long reach 10G-TDM-OCDM-PON sysems were measured in wo sages. Firs, he oal ransmission performance was evaluaed under he condiion of fixing he por numbers of muli-por encoder/decoders. Figure 5.6 shows he experimenal seup and resuls of full duplex 4-packe 4-OC ransmission over a 65-km SMF wihou dispersion compensaion on a single wavelengh. Four differen ransmission lenghs (25, 15, 10, and 1 km) beween an RN and ONUs were esed because he pracical 10-Gb/s TDM-PON sysem is operaed under various access spans wihin 20 km [39]. For BER measuremens of differen ransmission disances, he connecions beween access spans and ONUs were changed a he connecion poins for he firs experimen, as shown in Fig. 5.6. In his experimen, a 16 16 por encoder/decoders pair was adoped as he muli-por encoder/decoder. Por names of D1, D2, D3, D4, U1, U2, U3, U4, D, and U were se o por numbers No. 1, 5, 9, 13, 3, 7, 11, 15, 8, and 6, respecively. Mode-locked laser diodes (MLLDs) wih a 10.3125 GHz repeiion rae and 1551 nm cener wavelengh were used for he OLT and ONUs, respecively. The 10-Gb/s burs-mode 3R receivers (BM-Rxs) were placed a he OLT. Use of he same wavelengh for boh uplink and downlink was he mos serious condiion due o reflecions from each componen. In he downlink, he MLLD oupu a 2.4-ps pulse rain, as shown in Fig. 5.6(a). I was modulaed o he coninuous daa wih PRBS 2 31 1 by a LiNbO 3 inensiy modulaor (LN-IM). The modulaed daa was spli ino 4 branches and encoded by he 16-chip (200 Gchip/s), 16-phase-shifed muli-por encoder wih 200-GHz FSR, as shown in Fig. 5.6(b). In order o reduce he chromaic dispersion effec, he specrum of each OC signal was ailored by filering ou he sideband componens by using he recangular shaped NB-OBPF wih a 1.6 nm bandwidh, as shown in Fig. 5.6(c). Figure 5.6(d) shows he compleely closed eye diagram of 4-OC daa afer 40-km SMF ransmission due o he chromaic dispersion. However, a good eye opening was obained from he muli-por decoder, which has he same srucure as he OLT muli-por encoder, a he RN (Fig. 5.6(e)) because he decoded signal has a single specrum componen. A he ONU, a clear eye diagram afer he oal 65-km SMF ransmission was achieved, as shown in Fig. 5.6(f). For he BER measuremen, he ransmied signal was recovered by he 3R receiver, as shown in Fig. 5.6(g). In his experimen, he

58 Chaper 5. Long Reach 10G-TDM-OCDM-PON Sysem 10-Gb/s burs-mode 3R receiver for he OLT was also applied for ONUs o measure he penaly beween uplink and downlink. In he uplink, 3.2-ps opical pulses were generaed by he MLLD, as shown in Fig. 5.6(h). The oupu of he MLLD was modulaed o 4 opical packes wih PRBS 2 31 1 daa by he burs-mode modulaors. Each burs-mode modulaor was consruced by boh a LN-IM and an acouso-opic modulaor (AOM). The swiching speed and he exincion raio of he AOMs were abou 100 ns and over 45 db, respecively. Therefore, he burs-mode modulaors could simulaneously achieve a fas burs urn-on/off ime and sufficien power suppression during idle periods. The packe lengh was 100 s wih an overhead lengh of 800 ns, which is complian wih IEEE802.3av sandards (Fig. 5.6(i)). These opical packes were combined and each guard ime beween packes was se o less han 300 ns. Oher uplink signals were also modulaed o he coninuous daa wih PRBS 2 31 1 due o a lack of equipmen. However, his experimenal seup is sufficien o demonsrae he feasibiliy of his sysem. Figure 5.6(j) shows he pulse broadening waveform afer 25-km SMF ransmission due o he chromaic dispersion. However, he envelope of he muli-por encoder oupu was shaped like a downlink opical encoded waveform, as shown in Fig. 5.6(k). Figure 5.6(l) shows ha he specrum of 4-OC daa was limied o only 4 specrum componens as he downlink. Afer 40-km SMF ransmission, 4-OC daa were decoded and recovered for BER measuremen by he muli-por decoder and burs-mode 3R receiver a he OLT, as shown in Figs. 5.6(m) and (n), respecively. The 10-Gb/s burs-mode 3R receiver can provide a burs-mode 3R funcion wih 82.5 Gsample/s over-sampling. Figures 5.7 and 5.8 show he BER measuremen resuls of he downlink and uplink, respecively. The solid and dashed lines indicae SMF ransmission and B-o-B resuls, respecively. In all cases, a BER of less han 10-7 could be achieved. This demonsraes ha he sysem can realize error-free operaion wih he forward error correcion (FEC) of RS (255, 223). In he cases of boh downlink and uplink, he power penalies increased wih furher SMF ransmission due o he increase of cumulaive chromaic dispersion as well as opical signal o noise raio (OSNR) degradaion. In conras, in he uplink, he power penaly beween packes for he same OC a BER = 10-3 was as low as 0.3 db because he burs-mode 3R receiver could recover he received packe daa quickly. A receiver sensiiviy of less han 29.8 dbm a BER = 10-3 was also achieved.

5.3. Full-Dulplex Transmission Experimen wihou Dispersion Compensaion 59 10 db/div Downlink (a) (n) 10.3125 GHz MLLD 1551 nm 20ps/div 50 ps/div 1 nm/div BM-ED BM-ED BM-ED BM-ED 10 db/div PRBS 2 31-1 20 ps/div (a) (n) (b) (c) (d) (e) PPG LN-IM 10 db/div OLT BM-Rx BM-Rx BM-Rx BM-Rx (m) 20 ps/div 1 nm/div (m) 20 ps/div 0.3 nm/div D1 D2 D3 D4 U1 U2 U3 U4 10 db/div Muli-por en/decoder NB-OBPF D 1.6 nm (b) U SMF 40 km 20 ps/div 1.6 nm 1 nm/div 10 db/div (l) (c) SMF 40 km SMF 40 km 20 ps/div 1.6 nm 1 nm/div 10 db/div 20 ps/div 0.3 nm/div 10 db/div 20 ps/div 0.3 nm/div SMF 25 km ONU #1-1 Remoe node SMF Rx ED (e) (f) (g) 25 km Muli-por D1 BM-Mod. en/decoder U1 (i) (d) (j) D2 15 km D ONU #1-4 U2 Gae Daa (k) BM-PPG 10 km 1.6 nm U D3 (l) U3 LN-IM NB-OBPF PRBS 2 D4 1 km 31-1 PPG U4 10 db/div (k) 20ps/div 20 ps/div 1 nm/div (j) 20 ps/div SMF 25 km (f) (i) 100 s (g) 20 ps/div 20 ps/div 50 s/div 20 ps/div 10 db/div 1551 nm MLLD (h) (h) 10.3125 GHz Connecion poins for firs experimen Connecion poins for second experimen Uplink 50 ps/div 1 nm/div Fig. 5.6: Experimenal seup and resuls of 10G-TDM-OCDM-PON full-duplex ransmission over 65-km SMF. Log(BER) Bi Error Raio -2 1E-2-3 1E-3-4 1E-4-5 1E-5-6 1E-6 1E-7 1E-8 1E-9 B-o-B -10-34 -32-30 -28-26 -24-22 -20-18 -16-14 Received Opical Power (dbm) Received opical power (dbm) 1E-10 D1: 65-km SMF D2: 55-km SMF D3: 50-km SMF D4: 41-km SMF Fig. 5.7: Measured BER performances of downlink 4-OC daa.